Replace Command with a new Task API with chain support

core/src/element.rs

@@ -10,7 +10,6 @@ use crate::{
     Widget,
 };
 
-use std::any::Any;
 use std::borrow::Borrow;
 
 /// A generic [`Widget`].
@@ -305,63 +304,9 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<B>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
-        struct MapOperation<'a, B> {
-            operation: &'a mut dyn widget::Operation<B>,
-        }
-
-        impl<'a, T, B> widget::Operation<T> for MapOperation<'a, B> {
-            fn container(
-                &mut self,
-                id: Option<&widget::Id>,
-                bounds: Rectangle,
-                operate_on_children: &mut dyn FnMut(
-                    &mut dyn widget::Operation<T>,
-                ),
-            ) {
-                self.operation.container(id, bounds, &mut |operation| {
-                    operate_on_children(&mut MapOperation { operation });
-                });
-            }
-
-            fn focusable(
-                &mut self,
-                state: &mut dyn widget::operation::Focusable,
-                id: Option<&widget::Id>,
-            ) {
-                self.operation.focusable(state, id);
-            }
-
-            fn scrollable(
-                &mut self,
-                state: &mut dyn widget::operation::Scrollable,
-                id: Option<&widget::Id>,
-                bounds: Rectangle,
-                translation: Vector,
-            ) {
-                self.operation.scrollable(state, id, bounds, translation);
-            }
-
-            fn text_input(
-                &mut self,
-                state: &mut dyn widget::operation::TextInput,
-                id: Option<&widget::Id>,
-            ) {
-                self.operation.text_input(state, id);
-            }
-
-            fn custom(&mut self, state: &mut dyn Any, id: Option<&widget::Id>) {
-                self.operation.custom(state, id);
-            }
-        }
-
-        self.widget.operate(
-            tree,
-            layout,
-            renderer,
-            &mut MapOperation { operation },
-        );
+        self.widget.operate(tree, layout, renderer, operation);
     }
 
     fn on_event(
@@ -495,7 +440,7 @@ where
         state: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         self.element
             .widget

core/src/lib.rs

@@ -35,6 +35,7 @@ mod color;
 mod content_fit;
 mod element;
 mod length;
+mod maybe;
 mod padding;
 mod pixels;
 mod point;
@@ -59,6 +60,7 @@ pub use font::Font;
 pub use gradient::Gradient;
 pub use layout::Layout;
 pub use length::Length;
+pub use maybe::{MaybeSend, MaybeSync};
 pub use overlay::Overlay;
 pub use padding::Padding;
 pub use pixels::Pixels;

core/src/overlay.rs

@@ -41,7 +41,7 @@ where
         &mut self,
         _layout: Layout<'_>,
         _renderer: &Renderer,
-        _operation: &mut dyn widget::Operation<Message>,
+        _operation: &mut dyn widget::Operation<()>,
     ) {
     }
 

core/src/overlay/element.rs

@@ -5,9 +5,7 @@ use crate::layout;
 use crate::mouse;
 use crate::renderer;
 use crate::widget;
-use crate::{Clipboard, Layout, Point, Rectangle, Shell, Size, Vector};
-
-use std::any::Any;
+use crate::{Clipboard, Layout, Point, Rectangle, Shell, Size};
 
 /// A generic [`Overlay`].
 #[allow(missing_debug_implementations)]
@@ -94,7 +92,7 @@ where
         &mut self,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         self.overlay.operate(layout, renderer, operation);
     }
@@ -146,59 +144,9 @@ where
         &mut self,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<B>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
-        struct MapOperation<'a, B> {
-            operation: &'a mut dyn widget::Operation<B>,
-        }
-
-        impl<'a, T, B> widget::Operation<T> for MapOperation<'a, B> {
-            fn container(
-                &mut self,
-                id: Option<&widget::Id>,
-                bounds: Rectangle,
-                operate_on_children: &mut dyn FnMut(
-                    &mut dyn widget::Operation<T>,
-                ),
-            ) {
-                self.operation.container(id, bounds, &mut |operation| {
-                    operate_on_children(&mut MapOperation { operation });
-                });
-            }
-
-            fn focusable(
-                &mut self,
-                state: &mut dyn widget::operation::Focusable,
-                id: Option<&widget::Id>,
-            ) {
-                self.operation.focusable(state, id);
-            }
-
-            fn scrollable(
-                &mut self,
-                state: &mut dyn widget::operation::Scrollable,
-                id: Option<&widget::Id>,
-                bounds: Rectangle,
-                translation: Vector,
-            ) {
-                self.operation.scrollable(state, id, bounds, translation);
-            }
-
-            fn text_input(
-                &mut self,
-                state: &mut dyn widget::operation::TextInput,
-                id: Option<&widget::Id>,
-            ) {
-                self.operation.text_input(state, id);
-            }
-
-            fn custom(&mut self, state: &mut dyn Any, id: Option<&widget::Id>) {
-                self.operation.custom(state, id);
-            }
-        }
-
-        self.content
-            .operate(layout, renderer, &mut MapOperation { operation });
+        self.content.operate(layout, renderer, operation);
     }
 
     fn on_event(

core/src/overlay/group.rs

@@ -132,7 +132,7 @@ where
         &mut self,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         operation.container(None, layout.bounds(), &mut |operation| {
             self.children.iter_mut().zip(layout.children()).for_each(

core/src/widget.rs

@@ -105,7 +105,7 @@ where
         _state: &mut Tree,
         _layout: Layout<'_>,
         _renderer: &Renderer,
-        _operation: &mut dyn Operation<Message>,
+        _operation: &mut dyn Operation<()>,
     ) {
     }
 

core/src/widget/operation.rs

@@ -8,15 +8,15 @@ pub use scrollable::Scrollable;
 pub use text_input::TextInput;
 
 use crate::widget::Id;
-use crate::{Rectangle, Vector};
+use crate::{MaybeSend, Rectangle, Vector};
 
 use std::any::Any;
 use std::fmt;
-use std::rc::Rc;
+use std::sync::Arc;
 
 /// A piece of logic that can traverse the widget tree of an application in
 /// order to query or update some widget state.
-pub trait Operation<T> {
+pub trait Operation<T>: MaybeSend {
     /// Operates on a widget that contains other widgets.
     ///
     /// The `operate_on_children` function can be called to return control to
@@ -81,7 +81,7 @@ where
 /// Maps the output of an [`Operation`] using the given function.
 pub fn map<A, B>(
     operation: Box<dyn Operation<A>>,
-    f: impl Fn(A) -> B + 'static,
+    f: impl Fn(A) -> B + Send + Sync + 'static,
 ) -> impl Operation<B>
 where
     A: 'static,
@@ -90,7 +90,7 @@ where
     #[allow(missing_debug_implementations)]
     struct Map<A, B> {
         operation: Box<dyn Operation<A>>,
-        f: Rc<dyn Fn(A) -> B>,
+        f: Arc<dyn Fn(A) -> B + Send + Sync>,
     }
 
     impl<A, B> Operation<B> for Map<A, B>
@@ -197,7 +197,7 @@ where
 
     Map {
         operation,
-        f: Rc::new(f),
+        f: Arc::new(f),
     }
 }
 

examples/editor/src/main.rs

@@ -4,7 +4,7 @@ use iced::widget::{
     button, column, container, horizontal_space, pick_list, row, text,
     text_editor, tooltip,
 };
-use iced::{Alignment, Command, Element, Font, Length, Subscription, Theme};
+use iced::{Alignment, Element, Font, Length, Subscription, Task, Theme};
 
 use std::ffi;
 use std::io;
@@ -51,26 +51,26 @@ impl Editor {
         }
     }
 
-    fn load() -> Command<Message> {
-        Command::perform(
+    fn load() -> Task<Message> {
+        Task::perform(
             load_file(format!("{}/src/main.rs", env!("CARGO_MANIFEST_DIR"))),
             Message::FileOpened,
         )
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::ActionPerformed(action) => {
                 self.is_dirty = self.is_dirty || action.is_edit();
 
                 self.content.perform(action);
 
-                Command::none()
+                Task::none()
             }
             Message::ThemeSelected(theme) => {
                 self.theme = theme;
 
-                Command::none()
+                Task::none()
             }
             Message::NewFile => {
                 if !self.is_loading {
@@ -78,15 +78,15 @@ impl Editor {
                     self.content = text_editor::Content::new();
                 }
 
-                Command::none()
+                Task::none()
             }
             Message::OpenFile => {
                 if self.is_loading {
-                    Command::none()
+                    Task::none()
                 } else {
                     self.is_loading = true;
 
-                    Command::perform(open_file(), Message::FileOpened)
+                    Task::perform(open_file(), Message::FileOpened)
                 }
             }
             Message::FileOpened(result) => {
@@ -98,15 +98,15 @@ impl Editor {
                     self.content = text_editor::Content::with_text(&contents);
                 }
 
-                Command::none()
+                Task::none()
             }
             Message::SaveFile => {
                 if self.is_loading {
-                    Command::none()
+                    Task::none()
                 } else {
                     self.is_loading = true;
 
-                    Command::perform(
+                    Task::perform(
                         save_file(self.file.clone(), self.content.text()),
                         Message::FileSaved,
                     )
@@ -120,7 +120,7 @@ impl Editor {
                     self.is_dirty = false;
                 }
 
-                Command::none()
+                Task::none()
             }
         }
     }

examples/events/src/main.rs

@@ -2,7 +2,7 @@ use iced::alignment;
 use iced::event::{self, Event};
 use iced::widget::{button, center, checkbox, text, Column};
 use iced::window;
-use iced::{Alignment, Command, Element, Length, Subscription};
+use iced::{Alignment, Element, Length, Subscription, Task};
 
 pub fn main() -> iced::Result {
     iced::program("Events - Iced", Events::update, Events::view)
@@ -25,7 +25,7 @@ enum Message {
 }
 
 impl Events {
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::EventOccurred(event) if self.enabled => {
                 self.last.push(event);
@@ -34,19 +34,19 @@ impl Events {
                     let _ = self.last.remove(0);
                 }
 
-                Command::none()
+                Task::none()
             }
             Message::EventOccurred(event) => {
                 if let Event::Window(window::Event::CloseRequested) = event {
                     window::close(window::Id::MAIN)
                 } else {
-                    Command::none()
+                    Task::none()
                 }
             }
             Message::Toggled(enabled) => {
                 self.enabled = enabled;
 
-                Command::none()
+                Task::none()
             }
             Message::Exit => window::close(window::Id::MAIN),
         }

examples/exit/src/main.rs

@@ -1,6 +1,6 @@
 use iced::widget::{button, center, column};
 use iced::window;
-use iced::{Alignment, Command, Element};
+use iced::{Alignment, Element, Task};
 
 pub fn main() -> iced::Result {
     iced::program("Exit - Iced", Exit::update, Exit::view).run()
@@ -18,13 +18,13 @@ enum Message {
 }
 
 impl Exit {
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::Confirm => window::close(window::Id::MAIN),
             Message::Exit => {
                 self.show_confirm = true;
 
-                Command::none()
+                Task::none()
             }
         }
     }

examples/game_of_life/src/main.rs

@@ -9,7 +9,7 @@ use iced::time;
 use iced::widget::{
     button, checkbox, column, container, pick_list, row, slider, text,
 };
-use iced::{Alignment, Command, Element, Length, Subscription, Theme};
+use iced::{Alignment, Element, Length, Subscription, Task, Theme};
 use std::time::Duration;
 
 pub fn main() -> iced::Result {
@@ -56,7 +56,7 @@ impl GameOfLife {
         }
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::Grid(message, version) => {
                 if version == self.version {
@@ -75,7 +75,7 @@ impl GameOfLife {
 
                     let version = self.version;
 
-                    return Command::perform(task, move |message| {
+                    return Task::perform(task, move |message| {
                         Message::Grid(message, version)
                     });
                 }
@@ -103,7 +103,7 @@ impl GameOfLife {
             }
         }
 
-        Command::none()
+        Task::none()
     }
 
     fn subscription(&self) -> Subscription<Message> {

examples/integration/src/controls.rs

@@ -2,7 +2,7 @@ use iced_wgpu::Renderer;
 use iced_widget::{column, container, row, slider, text, text_input};
 use iced_winit::core::alignment;
 use iced_winit::core::{Color, Element, Length, Theme};
-use iced_winit::runtime::{Command, Program};
+use iced_winit::runtime::{Program, Task};
 
 pub struct Controls {
     background_color: Color,
@@ -33,7 +33,7 @@ impl Program for Controls {
     type Message = Message;
     type Renderer = Renderer;
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::BackgroundColorChanged(color) => {
                 self.background_color = color;
@@ -43,7 +43,7 @@ impl Program for Controls {
             }
         }
 
-        Command::none()
+        Task::none()
     }
 
     fn view(&self) -> Element<Message, Theme, Renderer> {

examples/loading_spinners/src/easing.rs

@@ -119,10 +119,7 @@ impl Builder {
 
     fn point(p: impl Into<Point>) -> lyon_algorithms::geom::Point<f32> {
         let p: Point = p.into();
-        lyon_algorithms::geom::point(
-            p.x.min(1.0).max(0.0),
-            p.y.min(1.0).max(0.0),
-        )
+        lyon_algorithms::geom::point(p.x.clamp(0.0, 1.0), p.y.clamp(0.0, 1.0))
     }
 }
 

examples/modal/src/main.rs

@@ -5,7 +5,7 @@ use iced::widget::{
     self, button, center, column, container, horizontal_space, mouse_area,
     opaque, pick_list, row, stack, text, text_input,
 };
-use iced::{Alignment, Color, Command, Element, Length, Subscription};
+use iced::{Alignment, Color, Element, Length, Subscription, Task};
 
 use std::fmt;
 
@@ -39,7 +39,7 @@ impl App {
         event::listen().map(Message::Event)
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::ShowModal => {
                 self.show_modal = true;
@@ -47,26 +47,26 @@ impl App {
             }
             Message::HideModal => {
                 self.hide_modal();
-                Command::none()
+                Task::none()
             }
             Message::Email(email) => {
                 self.email = email;
-                Command::none()
+                Task::none()
             }
             Message::Password(password) => {
                 self.password = password;
-                Command::none()
+                Task::none()
             }
             Message::Plan(plan) => {
                 self.plan = plan;
-                Command::none()
+                Task::none()
             }
             Message::Submit => {
                 if !self.email.is_empty() && !self.password.is_empty() {
                     self.hide_modal();
                 }
 
-                Command::none()
+                Task::none()
             }
             Message::Event(event) => match event {
                 Event::Keyboard(keyboard::Event::KeyPressed {
@@ -85,9 +85,9 @@ impl App {
                     ..
                 }) => {
                     self.hide_modal();
-                    Command::none()
+                    Task::none()
                 }
-                _ => Command::none(),
+                _ => Task::none(),
             },
         }
     }

examples/multi_window/src/main.rs

@@ -6,7 +6,7 @@ use iced::widget::{
 };
 use iced::window;
 use iced::{
-    Alignment, Command, Element, Length, Point, Settings, Subscription, Theme,
+    Alignment, Element, Length, Point, Settings, Subscription, Task, Theme,
     Vector,
 };
 
@@ -48,13 +48,13 @@ impl multi_window::Application for Example {
     type Theme = Theme;
     type Flags = ();
 
-    fn new(_flags: ()) -> (Self, Command<Message>) {
+    fn new(_flags: ()) -> (Self, Task<Message>) {
         (
             Example {
                 windows: HashMap::from([(window::Id::MAIN, Window::new(1))]),
                 next_window_pos: window::Position::Default,
             },
-            Command::none(),
+            Task::none(),
         )
     }
 
@@ -65,14 +65,14 @@ impl multi_window::Application for Example {
             .unwrap_or("Example".to_string())
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::ScaleInputChanged(id, scale) => {
                 let window =
                     self.windows.get_mut(&id).expect("Window not found!");
                 window.scale_input = scale;
 
-                Command::none()
+                Task::none()
             }
             Message::ScaleChanged(id, scale) => {
                 let window =
@@ -83,7 +83,7 @@ impl multi_window::Application for Example {
                     .unwrap_or(window.current_scale)
                     .clamp(0.5, 5.0);
 
-                Command::none()
+                Task::none()
             }
             Message::TitleChanged(id, title) => {
                 let window =
@@ -91,12 +91,12 @@ impl multi_window::Application for Example {
 
                 window.title = title;
 
-                Command::none()
+                Task::none()
             }
             Message::CloseWindow(id) => window::close(id),
             Message::WindowClosed(id) => {
                 self.windows.remove(&id);
-                Command::none()
+                Task::none()
             }
             Message::WindowOpened(id, position) => {
                 if let Some(position) = position {
@@ -108,13 +108,13 @@ impl multi_window::Application for Example {
                 if let Some(window) = self.windows.get(&id) {
                     text_input::focus(window.input_id.clone())
                 } else {
-                    Command::none()
+                    Task::none()
                 }
             }
             Message::NewWindow => {
                 let count = self.windows.len() + 1;
 
-                let (id, spawn_window) = window::spawn(window::Settings {
+                let (id, spawn_window) = window::open(window::Settings {
                     position: self.next_window_pos,
                     exit_on_close_request: count % 2 == 0,
                     ..Default::default()

examples/pokedex/src/main.rs

@@ -1,6 +1,6 @@
 use iced::futures;
 use iced::widget::{self, center, column, image, row, text};
-use iced::{Alignment, Command, Element, Length};
+use iced::{Alignment, Element, Length, Task};
 
 pub fn main() -> iced::Result {
     iced::program(Pokedex::title, Pokedex::update, Pokedex::view)
@@ -25,8 +25,8 @@ enum Message {
 }
 
 impl Pokedex {
-    fn search() -> Command<Message> {
-        Command::perform(Pokemon::search(), Message::PokemonFound)
+    fn search() -> Task<Message> {
+        Task::perform(Pokemon::search(), Message::PokemonFound)
     }
 
     fn title(&self) -> String {
@@ -39,20 +39,20 @@ impl Pokedex {
         format!("{subtitle} - Pokédex")
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::PokemonFound(Ok(pokemon)) => {
                 *self = Pokedex::Loaded { pokemon };
 
-                Command::none()
+                Task::none()
             }
             Message::PokemonFound(Err(_error)) => {
                 *self = Pokedex::Errored;
 
-                Command::none()
+                Task::none()
             }
             Message::Search => match self {
-                Pokedex::Loading => Command::none(),
+                Pokedex::Loading => Task::none(),
                 _ => {
                     *self = Pokedex::Loading;
 

examples/screenshot/src/main.rs

@@ -4,7 +4,7 @@ use iced::widget::{button, column, container, image, row, text, text_input};
 use iced::window;
 use iced::window::screenshot::{self, Screenshot};
 use iced::{
-    Alignment, Command, ContentFit, Element, Length, Rectangle, Subscription,
+    Alignment, ContentFit, Element, Length, Rectangle, Subscription, Task,
 };
 
 use ::image as img;
@@ -44,13 +44,11 @@ enum Message {
 }
 
 impl Example {
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::Screenshot => {
-                return iced::window::screenshot(
-                    window::Id::MAIN,
-                    Message::ScreenshotData,
-                );
+                return iced::window::screenshot(window::Id::MAIN)
+                    .map(Message::ScreenshotData);
             }
             Message::ScreenshotData(screenshot) => {
                 self.screenshot = Some(screenshot);
@@ -59,7 +57,7 @@ impl Example {
                 if let Some(screenshot) = &self.screenshot {
                     self.png_saving = true;
 
-                    return Command::perform(
+                    return Task::perform(
                         save_to_png(screenshot.clone()),
                         Message::PngSaved,
                     );
@@ -103,7 +101,7 @@ impl Example {
             }
         }
 
-        Command::none()
+        Task::none()
     }
 
     fn view(&self) -> Element<'_, Message> {

examples/scrollable/src/main.rs

@@ -3,7 +3,7 @@ use iced::widget::{
     button, column, container, horizontal_space, progress_bar, radio, row,
     scrollable, slider, text, vertical_space, Scrollable,
 };
-use iced::{Alignment, Border, Color, Command, Element, Length, Theme};
+use iced::{Alignment, Border, Color, Element, Length, Task, Theme};
 
 use once_cell::sync::Lazy;
 
@@ -59,7 +59,7 @@ impl ScrollableDemo {
         }
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::SwitchDirection(direction) => {
                 self.current_scroll_offset = scrollable::RelativeOffset::START;
@@ -82,17 +82,17 @@ impl ScrollableDemo {
             Message::ScrollbarWidthChanged(width) => {
                 self.scrollbar_width = width;
 
-                Command::none()
+                Task::none()
             }
             Message::ScrollbarMarginChanged(margin) => {
                 self.scrollbar_margin = margin;
 
-                Command::none()
+                Task::none()
             }
             Message::ScrollerWidthChanged(width) => {
                 self.scroller_width = width;
 
-                Command::none()
+                Task::none()
             }
             Message::ScrollToBeginning => {
                 self.current_scroll_offset = scrollable::RelativeOffset::START;
@@ -113,7 +113,7 @@ impl ScrollableDemo {
             Message::Scrolled(viewport) => {
                 self.current_scroll_offset = viewport.relative_offset();
 
-                Command::none()
+                Task::none()
             }
         }
     }

examples/system_information/src/main.rs

@@ -1,5 +1,5 @@
 use iced::widget::{button, center, column, text};
-use iced::{system, Command, Element};
+use iced::{system, Element, Task};
 
 pub fn main() -> iced::Result {
     iced::program("System Information - Iced", Example::update, Example::view)
@@ -24,19 +24,20 @@ enum Message {
 }
 
 impl Example {
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::Refresh => {
                 *self = Self::Loading;
 
-                return system::fetch_information(Message::InformationReceived);
+                return system::fetch_information()
+                    .map(Message::InformationReceived);
             }
             Message::InformationReceived(information) => {
                 *self = Self::Loaded { information };
             }
         }
 
-        Command::none()
+        Task::none()
     }
 
     fn view(&self) -> Element<Message> {

examples/toast/src/main.rs

@@ -4,7 +4,7 @@ use iced::keyboard::key;
 use iced::widget::{
     self, button, center, column, pick_list, row, slider, text, text_input,
 };
-use iced::{Alignment, Command, Element, Length, Subscription};
+use iced::{Alignment, Element, Length, Subscription, Task};
 
 use toast::{Status, Toast};
 
@@ -49,7 +49,7 @@ impl App {
         event::listen().map(Message::Event)
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::Add => {
                 if !self.editing.title.is_empty()
@@ -57,27 +57,27 @@ impl App {
                 {
                     self.toasts.push(std::mem::take(&mut self.editing));
                 }
-                Command::none()
+                Task::none()
             }
             Message::Close(index) => {
                 self.toasts.remove(index);
-                Command::none()
+                Task::none()
             }
             Message::Title(title) => {
                 self.editing.title = title;
-                Command::none()
+                Task::none()
             }
             Message::Body(body) => {
                 self.editing.body = body;
-                Command::none()
+                Task::none()
             }
             Message::Status(status) => {
                 self.editing.status = status;
-                Command::none()
+                Task::none()
             }
             Message::Timeout(timeout) => {
                 self.timeout_secs = timeout as u64;
-                Command::none()
+                Task::none()
             }
             Message::Event(Event::Keyboard(keyboard::Event::KeyPressed {
                 key: keyboard::Key::Named(key::Named::Tab),
@@ -88,7 +88,7 @@ impl App {
                 key: keyboard::Key::Named(key::Named::Tab),
                 ..
             })) => widget::focus_next(),
-            Message::Event(_) => Command::none(),
+            Message::Event(_) => Task::none(),
         }
     }
 
@@ -347,7 +347,7 @@ mod toast {
             state: &mut Tree,
             layout: Layout<'_>,
             renderer: &Renderer,
-            operation: &mut dyn Operation<Message>,
+            operation: &mut dyn Operation<()>,
         ) {
             operation.container(None, layout.bounds(), &mut |operation| {
                 self.content.as_widget().operate(
@@ -589,7 +589,7 @@ mod toast {
             &mut self,
             layout: Layout<'_>,
             renderer: &Renderer,
-            operation: &mut dyn widget::Operation<Message>,
+            operation: &mut dyn widget::Operation<()>,
         ) {
             operation.container(None, layout.bounds(), &mut |operation| {
                 self.toasts

examples/todos/src/main.rs

@@ -5,7 +5,7 @@ use iced::widget::{
     scrollable, text, text_input, Text,
 };
 use iced::window;
-use iced::{Command, Element, Font, Length, Subscription};
+use iced::{Element, Font, Length, Subscription, Task as Command};
 
 use once_cell::sync::Lazy;
 use serde::{Deserialize, Serialize};

examples/visible_bounds/src/main.rs

@@ -5,8 +5,8 @@ use iced::widget::{
 };
 use iced::window;
 use iced::{
-    Alignment, Color, Command, Element, Font, Length, Point, Rectangle,
-    Subscription, Theme,
+    Alignment, Color, Element, Font, Length, Point, Rectangle, Subscription,
+    Task, Theme,
 };
 
 pub fn main() -> iced::Result {
@@ -33,14 +33,14 @@ enum Message {
 }
 
 impl Example {
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::MouseMoved(position) => {
                 self.mouse_position = Some(position);
 
-                Command::none()
+                Task::none()
             }
-            Message::Scrolled | Message::WindowResized => Command::batch(vec![
+            Message::Scrolled | Message::WindowResized => Task::batch(vec![
                 container::visible_bounds(OUTER_CONTAINER.clone())
                     .map(Message::OuterBoundsFetched),
                 container::visible_bounds(INNER_CONTAINER.clone())
@@ -49,12 +49,12 @@ impl Example {
             Message::OuterBoundsFetched(outer_bounds) => {
                 self.outer_bounds = outer_bounds;
 
-                Command::none()
+                Task::none()
             }
             Message::InnerBoundsFetched(inner_bounds) => {
                 self.inner_bounds = inner_bounds;
 
-                Command::none()
+                Task::none()
             }
         }
     }

examples/websocket/src/main.rs

@@ -4,7 +4,7 @@ use iced::alignment::{self, Alignment};
 use iced::widget::{
     self, button, center, column, row, scrollable, text, text_input,
 };
-use iced::{color, Command, Element, Length, Subscription};
+use iced::{color, Element, Length, Subscription, Task};
 use once_cell::sync::Lazy;
 
 pub fn main() -> iced::Result {
@@ -30,19 +30,19 @@ enum Message {
 }
 
 impl WebSocket {
-    fn load() -> Command<Message> {
-        Command::batch([
-            Command::perform(echo::server::run(), |_| Message::Server),
+    fn load() -> Task<Message> {
+        Task::batch([
+            Task::perform(echo::server::run(), |_| Message::Server),
             widget::focus_next(),
         ])
     }
 
-    fn update(&mut self, message: Message) -> Command<Message> {
+    fn update(&mut self, message: Message) -> Task<Message> {
         match message {
             Message::NewMessageChanged(new_message) => {
                 self.new_message = new_message;
 
-                Command::none()
+                Task::none()
             }
             Message::Send(message) => match &mut self.state {
                 State::Connected(connection) => {
@@ -50,9 +50,9 @@ impl WebSocket {
 
                     connection.send(message);
 
-                    Command::none()
+                    Task::none()
                 }
-                State::Disconnected => Command::none(),
+                State::Disconnected => Task::none(),
             },
             Message::Echo(event) => match event {
                 echo::Event::Connected(connection) => {
@@ -60,14 +60,14 @@ impl WebSocket {
 
                     self.messages.push(echo::Message::connected());
 
-                    Command::none()
+                    Task::none()
                 }
                 echo::Event::Disconnected => {
                     self.state = State::Disconnected;
 
                     self.messages.push(echo::Message::disconnected());
 
-                    Command::none()
+                    Task::none()
                 }
                 echo::Event::MessageReceived(message) => {
                     self.messages.push(message);
@@ -78,7 +78,7 @@ impl WebSocket {
                     )
                 }
             },
-            Message::Server => Command::none(),
+            Message::Server => Task::none(),
         }
     }
 

futures/src/event.rs

@@ -1,8 +1,8 @@
 //! Listen to runtime events.
 use crate::core::event::{self, Event};
 use crate::core::window;
+use crate::core::MaybeSend;
 use crate::subscription::{self, Subscription};
-use crate::MaybeSend;
 
 /// Returns a [`Subscription`] to all the ignored runtime events.
 ///

futures/src/executor.rs

@@ -1,5 +1,5 @@
 //! Choose your preferred executor to power a runtime.
-use crate::MaybeSend;
+use crate::core::MaybeSend;
 use futures::Future;
 
 /// A type that can run futures.

futures/src/keyboard.rs

@@ -2,8 +2,8 @@
 use crate::core;
 use crate::core::event;
 use crate::core::keyboard::{Event, Key, Modifiers};
+use crate::core::MaybeSend;
 use crate::subscription::{self, Subscription};
-use crate::MaybeSend;
 
 /// Listens to keyboard key presses and calls the given function
 /// map them into actual messages.

futures/src/lib.rs

@@ -8,7 +8,6 @@
 pub use futures;
 pub use iced_core as core;
 
-mod maybe;
 mod runtime;
 
 pub mod backend;
@@ -18,7 +17,6 @@ pub mod keyboard;
 pub mod subscription;
 
 pub use executor::Executor;
-pub use maybe::{MaybeSend, MaybeSync};
 pub use platform::*;
 pub use runtime::Runtime;
 pub use subscription::Subscription;

futures/src/runtime.rs

@@ -1,6 +1,7 @@
 //! Run commands and keep track of subscriptions.
+use crate::core::MaybeSend;
 use crate::subscription;
-use crate::{BoxFuture, BoxStream, Executor, MaybeSend};
+use crate::{BoxFuture, BoxStream, Executor};
 
 use futures::{channel::mpsc, Sink};
 use std::marker::PhantomData;

futures/src/subscription.rs

@@ -5,8 +5,9 @@ pub use tracker::Tracker;
 
 use crate::core::event;
 use crate::core::window;
+use crate::core::MaybeSend;
 use crate::futures::{Future, Stream};
-use crate::{BoxStream, MaybeSend};
+use crate::BoxStream;
 
 use futures::channel::mpsc;
 use futures::never::Never;

futures/src/subscription/tracker.rs

@@ -1,5 +1,6 @@
+use crate::core::MaybeSend;
 use crate::subscription::{Event, Hasher, Recipe};
-use crate::{BoxFuture, MaybeSend};
+use crate::BoxFuture;
 
 use futures::channel::mpsc;
 use futures::sink::{Sink, SinkExt};

graphics/src/compositor.rs

@@ -1,7 +1,6 @@
 //! A compositor is responsible for initializing a renderer and managing window
 //! surfaces.
-use crate::core::Color;
-use crate::futures::{MaybeSend, MaybeSync};
+use crate::core::{Color, MaybeSend, MaybeSync};
 use crate::{Error, Settings, Viewport};
 
 use raw_window_handle::{HasDisplayHandle, HasWindowHandle};

runtime/src/clipboard.rs

@@ -1,80 +1,62 @@
 //! Access the clipboard.
-use crate::command::{self, Command};
 use crate::core::clipboard::Kind;
-use crate::futures::MaybeSend;
+use crate::futures::futures::channel::oneshot;
+use crate::Task;
 
-use std::fmt;
-
-/// A clipboard action to be performed by some [`Command`].
+/// A clipboard action to be performed by some [`Task`].
 ///
-/// [`Command`]: crate::Command
-pub enum Action<T> {
+/// [`Task`]: crate::Task
+#[derive(Debug)]
+pub enum Action {
     /// Read the clipboard and produce `T` with the result.
-    Read(Box<dyn Fn(Option<String>) -> T>, Kind),
+    Read {
+        /// The clipboard target.
+        target: Kind,
+        /// The channel to send the read contents.
+        channel: oneshot::Sender<Option<String>>,
+    },
 
     /// Write the given contents to the clipboard.
-    Write(String, Kind),
-}
-
-impl<T> Action<T> {
-    /// Maps the output of a clipboard [`Action`] using the provided closure.
-    pub fn map<A>(
-        self,
-        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
-    ) -> Action<A>
-    where
-        T: 'static,
-    {
-        match self {
-            Self::Read(o, target) => {
-                Action::Read(Box::new(move |s| f(o(s))), target)
-            }
-            Self::Write(content, target) => Action::Write(content, target),
-        }
-    }
-}
-
-impl<T> fmt::Debug for Action<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::Read(_, target) => write!(f, "Action::Read{target:?}"),
-            Self::Write(_, target) => write!(f, "Action::Write({target:?})"),
-        }
-    }
+    Write {
+        /// The clipboard target.
+        target: Kind,
+        /// The contents to be written.
+        contents: String,
+    },
 }
 
 /// Read the current contents of the clipboard.
-pub fn read<Message>(
-    f: impl Fn(Option<String>) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Clipboard(Action::Read(
-        Box::new(f),
-        Kind::Standard,
-    )))
+pub fn read() -> Task<Option<String>> {
+    Task::oneshot(|channel| {
+        crate::Action::Clipboard(Action::Read {
+            target: Kind::Standard,
+            channel,
+        })
+    })
 }
 
 /// Read the current contents of the primary clipboard.
-pub fn read_primary<Message>(
-    f: impl Fn(Option<String>) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Clipboard(Action::Read(
-        Box::new(f),
-        Kind::Primary,
-    )))
+pub fn read_primary() -> Task<Option<String>> {
+    Task::oneshot(|channel| {
+        crate::Action::Clipboard(Action::Read {
+            target: Kind::Primary,
+            channel,
+        })
+    })
 }
 
 /// Write the given contents to the clipboard.
-pub fn write<Message>(contents: String) -> Command<Message> {
-    Command::single(command::Action::Clipboard(Action::Write(
+pub fn write<T>(contents: String) -> Task<T> {
+    Task::effect(crate::Action::Clipboard(Action::Write {
+        target: Kind::Standard,
         contents,
-        Kind::Standard,
-    )))
+    }))
 }
 
 /// Write the given contents to the primary clipboard.
-pub fn write_primary<Message>(contents: String) -> Command<Message> {
-    Command::single(command::Action::Clipboard(Action::Write(
+pub fn write_primary<Message>(contents: String) -> Task<Message> {
+    Task::effect(crate::Action::Clipboard(Action::Write {
+        target: Kind::Primary,
         contents,
-        Kind::Primary,
-    )))
+    }))
 }

runtime/src/command.rs

@@ -1,147 +0,0 @@
-//! Run asynchronous actions.
-mod action;
-
-pub use action::Action;
-
-use crate::core::widget;
-use crate::futures::futures;
-use crate::futures::MaybeSend;
-
-use futures::channel::mpsc;
-use futures::Stream;
-use std::fmt;
-use std::future::Future;
-
-/// A set of asynchronous actions to be performed by some runtime.
-#[must_use = "`Command` must be returned to runtime to take effect"]
-pub struct Command<T>(Internal<Action<T>>);
-
-#[derive(Debug)]
-enum Internal<T> {
-    None,
-    Single(T),
-    Batch(Vec<T>),
-}
-
-impl<T> Command<T> {
-    /// Creates an empty [`Command`].
-    ///
-    /// In other words, a [`Command`] that does nothing.
-    pub const fn none() -> Self {
-        Self(Internal::None)
-    }
-
-    /// Creates a [`Command`] that performs a single [`Action`].
-    pub const fn single(action: Action<T>) -> Self {
-        Self(Internal::Single(action))
-    }
-
-    /// Creates a [`Command`] that performs a [`widget::Operation`].
-    pub fn widget(operation: impl widget::Operation<T> + 'static) -> Self {
-        Self::single(Action::Widget(Box::new(operation)))
-    }
-
-    /// Creates a [`Command`] that performs the action of the given future.
-    pub fn perform<A>(
-        future: impl Future<Output = A> + 'static + MaybeSend,
-        f: impl FnOnce(A) -> T + 'static + MaybeSend,
-    ) -> Command<T> {
-        use futures::FutureExt;
-
-        Command::single(Action::Future(Box::pin(future.map(f))))
-    }
-
-    /// Creates a [`Command`] that runs the given stream to completion.
-    pub fn run<A>(
-        stream: impl Stream<Item = A> + 'static + MaybeSend,
-        f: impl Fn(A) -> T + 'static + MaybeSend,
-    ) -> Command<T> {
-        use futures::StreamExt;
-
-        Command::single(Action::Stream(Box::pin(stream.map(f))))
-    }
-
-    /// Creates a [`Command`] that performs the actions of all the given
-    /// commands.
-    ///
-    /// Once this command is run, all the commands will be executed at once.
-    pub fn batch(commands: impl IntoIterator<Item = Command<T>>) -> Self {
-        let mut batch = Vec::new();
-
-        for Command(command) in commands {
-            match command {
-                Internal::None => {}
-                Internal::Single(command) => batch.push(command),
-                Internal::Batch(commands) => batch.extend(commands),
-            }
-        }
-
-        Self(Internal::Batch(batch))
-    }
-
-    /// Applies a transformation to the result of a [`Command`].
-    pub fn map<A>(
-        self,
-        f: impl Fn(T) -> A + 'static + MaybeSend + Sync + Clone,
-    ) -> Command<A>
-    where
-        T: 'static,
-        A: 'static,
-    {
-        match self.0 {
-            Internal::None => Command::none(),
-            Internal::Single(action) => Command::single(action.map(f)),
-            Internal::Batch(batch) => Command(Internal::Batch(
-                batch
-                    .into_iter()
-                    .map(|action| action.map(f.clone()))
-                    .collect(),
-            )),
-        }
-    }
-
-    /// Returns all of the actions of the [`Command`].
-    pub fn actions(self) -> Vec<Action<T>> {
-        let Command(command) = self;
-
-        match command {
-            Internal::None => Vec::new(),
-            Internal::Single(action) => vec![action],
-            Internal::Batch(batch) => batch,
-        }
-    }
-}
-
-impl<Message> From<()> for Command<Message> {
-    fn from(_value: ()) -> Self {
-        Self::none()
-    }
-}
-
-impl<T> fmt::Debug for Command<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        let Command(command) = self;
-
-        command.fmt(f)
-    }
-}
-
-/// Creates a [`Command`] that produces the `Message`s published from a [`Future`]
-/// to an [`mpsc::Sender`] with the given bounds.
-pub fn channel<Fut, Message>(
-    size: usize,
-    f: impl FnOnce(mpsc::Sender<Message>) -> Fut + MaybeSend + 'static,
-) -> Command<Message>
-where
-    Fut: Future<Output = ()> + MaybeSend + 'static,
-    Message: 'static + MaybeSend,
-{
-    use futures::future;
-    use futures::stream::{self, StreamExt};
-
-    let (sender, receiver) = mpsc::channel(size);
-
-    let runner = stream::once(f(sender)).filter_map(|_| future::ready(None));
-
-    Command::single(Action::Stream(Box::pin(stream::select(receiver, runner))))
-}

runtime/src/command/action.rs

@@ -1,100 +0,0 @@
-use crate::clipboard;
-use crate::core::widget;
-use crate::font;
-use crate::futures::MaybeSend;
-use crate::system;
-use crate::window;
-
-use std::any::Any;
-use std::borrow::Cow;
-use std::fmt;
-
-/// An action that a [`Command`] can perform.
-///
-/// [`Command`]: crate::Command
-pub enum Action<T> {
-    /// Run a [`Future`] to completion.
-    ///
-    /// [`Future`]: iced_futures::BoxFuture
-    Future(iced_futures::BoxFuture<T>),
-
-    /// Run a [`Stream`] to completion.
-    ///
-    /// [`Stream`]: iced_futures::BoxStream
-    Stream(iced_futures::BoxStream<T>),
-
-    /// Run a clipboard action.
-    Clipboard(clipboard::Action<T>),
-
-    /// Run a window action.
-    Window(window::Action<T>),
-
-    /// Run a system action.
-    System(system::Action<T>),
-
-    /// Run a widget action.
-    Widget(Box<dyn widget::Operation<T>>),
-
-    /// Load a font from its bytes.
-    LoadFont {
-        /// The bytes of the font to load.
-        bytes: Cow<'static, [u8]>,
-
-        /// The message to produce when the font has been loaded.
-        tagger: Box<dyn Fn(Result<(), font::Error>) -> T>,
-    },
-
-    /// A custom action supported by a specific runtime.
-    Custom(Box<dyn Any>),
-}
-
-impl<T> Action<T> {
-    /// Applies a transformation to the result of a [`Command`].
-    ///
-    /// [`Command`]: crate::Command
-    pub fn map<A>(
-        self,
-        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
-    ) -> Action<A>
-    where
-        A: 'static,
-        T: 'static,
-    {
-        use iced_futures::futures::{FutureExt, StreamExt};
-
-        match self {
-            Self::Future(future) => Action::Future(Box::pin(future.map(f))),
-            Self::Stream(stream) => Action::Stream(Box::pin(stream.map(f))),
-            Self::Clipboard(action) => Action::Clipboard(action.map(f)),
-            Self::Window(window) => Action::Window(window.map(f)),
-            Self::System(system) => Action::System(system.map(f)),
-            Self::Widget(operation) => {
-                Action::Widget(Box::new(widget::operation::map(operation, f)))
-            }
-            Self::LoadFont { bytes, tagger } => Action::LoadFont {
-                bytes,
-                tagger: Box::new(move |result| f(tagger(result))),
-            },
-            Self::Custom(custom) => Action::Custom(custom),
-        }
-    }
-}
-
-impl<T> fmt::Debug for Action<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::Future(_) => write!(f, "Action::Future"),
-            Self::Stream(_) => write!(f, "Action::Stream"),
-            Self::Clipboard(action) => {
-                write!(f, "Action::Clipboard({action:?})")
-            }
-            Self::Window(action) => {
-                write!(f, "Action::Window({action:?})")
-            }
-            Self::System(action) => write!(f, "Action::System({action:?})"),
-            Self::Widget(_action) => write!(f, "Action::Widget"),
-            Self::LoadFont { .. } => write!(f, "Action::LoadFont"),
-            Self::Custom(_) => write!(f, "Action::Custom"),
-        }
-    }
-}

runtime/src/font.rs

@@ -1,7 +1,5 @@
 //! Load and use fonts.
-pub use iced_core::font::*;
-
-use crate::command::{self, Command};
+use crate::{Action, Task};
 use std::borrow::Cow;
 
 /// An error while loading a font.
@@ -9,11 +7,9 @@ use std::borrow::Cow;
 pub enum Error {}
 
 /// Load a font from its bytes.
-pub fn load(
-    bytes: impl Into<Cow<'static, [u8]>>,
-) -> Command<Result<(), Error>> {
-    Command::single(command::Action::LoadFont {
+pub fn load(bytes: impl Into<Cow<'static, [u8]>>) -> Task<Result<(), Error>> {
+    Task::oneshot(|channel| Action::LoadFont {
         bytes: bytes.into(),
-        tagger: Box::new(std::convert::identity),
+        channel,
     })
 }

runtime/src/lib.rs

@@ -10,7 +10,6 @@
 )]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 pub mod clipboard;
-pub mod command;
 pub mod font;
 pub mod keyboard;
 pub mod overlay;
@@ -22,6 +21,8 @@ pub mod window;
 #[cfg(feature = "multi-window")]
 pub mod multi_window;
 
+mod task;
+
 // We disable debug capabilities on release builds unless the `debug` feature
 // is explicitly enabled.
 #[cfg(feature = "debug")]
@@ -34,8 +35,81 @@ mod debug;
 pub use iced_core as core;
 pub use iced_futures as futures;
 
-pub use command::Command;
 pub use debug::Debug;
-pub use font::Font;
 pub use program::Program;
+pub use task::Task;
 pub use user_interface::UserInterface;
+
+use crate::core::widget;
+use crate::futures::futures::channel::oneshot;
+
+use std::borrow::Cow;
+use std::fmt;
+
+/// An action that the iced runtime can perform.
+pub enum Action<T> {
+    /// Output some value.
+    Output(T),
+
+    /// Load a font from its bytes.
+    LoadFont {
+        /// The bytes of the font to load.
+        bytes: Cow<'static, [u8]>,
+        /// The channel to send back the load result.
+        channel: oneshot::Sender<Result<(), font::Error>>,
+    },
+
+    /// Run a widget operation.
+    Widget(Box<dyn widget::Operation<()> + Send>),
+
+    /// Run a clipboard action.
+    Clipboard(clipboard::Action),
+
+    /// Run a window action.
+    Window(window::Action),
+
+    /// Run a system action.
+    System(system::Action),
+}
+
+impl<T> Action<T> {
+    /// Creates a new [`Action::Widget`] with the given [`widget::Operation`].
+    pub fn widget(operation: impl widget::Operation<()> + 'static) -> Self {
+        Self::Widget(Box::new(operation))
+    }
+
+    fn output<O>(self) -> Result<T, Action<O>> {
+        match self {
+            Action::Output(output) => Ok(output),
+            Action::LoadFont { bytes, channel } => {
+                Err(Action::LoadFont { bytes, channel })
+            }
+            Action::Widget(operation) => Err(Action::Widget(operation)),
+            Action::Clipboard(action) => Err(Action::Clipboard(action)),
+            Action::Window(action) => Err(Action::Window(action)),
+            Action::System(action) => Err(Action::System(action)),
+        }
+    }
+}
+
+impl<T> fmt::Debug for Action<T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Action::Output(output) => write!(f, "Action::Output({output:?})"),
+            Action::LoadFont { .. } => {
+                write!(f, "Action::LoadFont")
+            }
+            Action::Widget { .. } => {
+                write!(f, "Action::Widget")
+            }
+            Action::Clipboard(action) => {
+                write!(f, "Action::Clipboard({action:?})")
+            }
+            Action::Window(_) => write!(f, "Action::Window"),
+            Action::System(action) => write!(f, "Action::System({action:?})"),
+        }
+    }
+}

runtime/src/multi_window/program.rs

@@ -2,7 +2,7 @@
 use crate::core::text;
 use crate::core::window;
 use crate::core::{Element, Renderer};
-use crate::Command;
+use crate::Task;
 
 /// The core of a user interface for a multi-window application following The Elm Architecture.
 pub trait Program: Sized {
@@ -21,9 +21,9 @@ pub trait Program: Sized {
     /// produced by either user interactions or commands, will be handled by
     /// this method.
     ///
-    /// Any [`Command`] returned will be executed immediately in the
-    /// background by shells.
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
+    /// Any [`Task`] returned will be executed immediately in the background by the
+    /// runtime.
+    fn update(&mut self, message: Self::Message) -> Task<Self::Message>;
 
     /// Returns the widgets to display in the [`Program`] for the `window`.
     ///

runtime/src/multi_window/state.rs

@@ -5,7 +5,7 @@ use crate::core::renderer;
 use crate::core::widget::operation::{self, Operation};
 use crate::core::{Clipboard, Size};
 use crate::user_interface::{self, UserInterface};
-use crate::{Command, Debug, Program};
+use crate::{Debug, Program, Task};
 
 /// The execution state of a multi-window [`Program`]. It leverages caching, event
 /// processing, and rendering primitive storage.
@@ -85,7 +85,7 @@ where
     /// the widgets of the linked [`Program`] if necessary.
     ///
     /// Returns a list containing the instances of [`Event`] that were not
-    /// captured by any widget, and the [`Command`] obtained from [`Program`]
+    /// captured by any widget, and the [`Task`] obtained from [`Program`]
     /// after updating it, only if an update was necessary.
     pub fn update(
         &mut self,
@@ -96,7 +96,7 @@ where
         style: &renderer::Style,
         clipboard: &mut dyn Clipboard,
         debug: &mut Debug,
-    ) -> (Vec<Event>, Option<Command<P::Message>>) {
+    ) -> (Vec<Event>, Option<Task<P::Message>>) {
         let mut user_interfaces = build_user_interfaces(
             &self.program,
             self.caches.take().unwrap(),
@@ -163,14 +163,14 @@ where
 
             drop(user_interfaces);
 
-            let commands = Command::batch(messages.into_iter().map(|msg| {
+            let commands = Task::batch(messages.into_iter().map(|msg| {
                 debug.log_message(&msg);
 
                 debug.update_started();
-                let command = self.program.update(msg);
+                let task = self.program.update(msg);
                 debug.update_finished();
 
-                command
+                task
             }));
 
             let mut user_interfaces = build_user_interfaces(
@@ -205,7 +205,7 @@ where
     pub fn operate(
         &mut self,
         renderer: &mut P::Renderer,
-        operations: impl Iterator<Item = Box<dyn Operation<P::Message>>>,
+        operations: impl Iterator<Item = Box<dyn Operation<()>>>,
         bounds: Size,
         debug: &mut Debug,
     ) {
@@ -227,9 +227,7 @@ where
 
                 match operation.finish() {
                     operation::Outcome::None => {}
-                    operation::Outcome::Some(message) => {
-                        self.queued_messages.push(message);
-                    }
+                    operation::Outcome::Some(()) => {}
                     operation::Outcome::Chain(next) => {
                         current_operation = Some(next);
                     }

runtime/src/overlay/nested.rs

@@ -131,13 +131,13 @@ where
         &mut self,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         fn recurse<Message, Theme, Renderer>(
             element: &mut overlay::Element<'_, Message, Theme, Renderer>,
             layout: Layout<'_>,
             renderer: &Renderer,
-            operation: &mut dyn widget::Operation<Message>,
+            operation: &mut dyn widget::Operation<()>,
         ) where
             Renderer: renderer::Renderer,
         {

runtime/src/program.rs

@@ -1,5 +1,5 @@
 //! Build interactive programs using The Elm Architecture.
-use crate::Command;
+use crate::Task;
 
 use iced_core::text;
 use iced_core::Element;
@@ -25,9 +25,9 @@ pub trait Program: Sized {
     /// produced by either user interactions or commands, will be handled by
     /// this method.
     ///
-    /// Any [`Command`] returned will be executed immediately in the
+    /// Any [`Task`] returned will be executed immediately in the
     /// background by shells.
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
+    fn update(&mut self, message: Self::Message) -> Task<Self::Message>;
 
     /// Returns the widgets to display in the [`Program`].
     ///

runtime/src/program/state.rs

@@ -4,7 +4,7 @@ use crate::core::renderer;
 use crate::core::widget::operation::{self, Operation};
 use crate::core::{Clipboard, Size};
 use crate::user_interface::{self, UserInterface};
-use crate::{Command, Debug, Program};
+use crate::{Debug, Program, Task};
 
 /// The execution state of a [`Program`]. It leverages caching, event
 /// processing, and rendering primitive storage.
@@ -84,7 +84,7 @@ where
     /// the widgets of the linked [`Program`] if necessary.
     ///
     /// Returns a list containing the instances of [`Event`] that were not
-    /// captured by any widget, and the [`Command`] obtained from [`Program`]
+    /// captured by any widget, and the [`Task`] obtained from [`Program`]
     /// after updating it, only if an update was necessary.
     pub fn update(
         &mut self,
@@ -95,7 +95,7 @@ where
         style: &renderer::Style,
         clipboard: &mut dyn Clipboard,
         debug: &mut Debug,
-    ) -> (Vec<Event>, Option<Command<P::Message>>) {
+    ) -> (Vec<Event>, Option<Task<P::Message>>) {
         let mut user_interface = build_user_interface(
             &mut self.program,
             self.cache.take().unwrap(),
@@ -129,7 +129,7 @@ where
         messages.append(&mut self.queued_messages);
         debug.event_processing_finished();
 
-        let command = if messages.is_empty() {
+        let task = if messages.is_empty() {
             debug.draw_started();
             self.mouse_interaction =
                 user_interface.draw(renderer, theme, style, cursor);
@@ -143,15 +143,14 @@ where
             // for now :^)
             let temp_cache = user_interface.into_cache();
 
-            let commands =
-                Command::batch(messages.into_iter().map(|message| {
+            let tasks = Task::batch(messages.into_iter().map(|message| {
                 debug.log_message(&message);
 
                 debug.update_started();
-                    let command = self.program.update(message);
+                let task = self.program.update(message);
                 debug.update_finished();
 
-                    command
+                task
             }));
 
             let mut user_interface = build_user_interface(
@@ -169,17 +168,17 @@ where
 
             self.cache = Some(user_interface.into_cache());
 
-            Some(commands)
+            Some(tasks)
         };
 
-        (uncaptured_events, command)
+        (uncaptured_events, task)
     }
 
     /// Applies [`Operation`]s to the [`State`]
     pub fn operate(
         &mut self,
         renderer: &mut P::Renderer,
-        operations: impl Iterator<Item = Box<dyn Operation<P::Message>>>,
+        operations: impl Iterator<Item = Box<dyn Operation<()>>>,
         bounds: Size,
         debug: &mut Debug,
     ) {
@@ -199,9 +198,7 @@ where
 
                 match operation.finish() {
                     operation::Outcome::None => {}
-                    operation::Outcome::Some(message) => {
-                        self.queued_messages.push(message);
-                    }
+                    operation::Outcome::Some(()) => {}
                     operation::Outcome::Chain(next) => {
                         current_operation = Some(next);
                     }

runtime/src/system.rs

@@ -1,6 +1,39 @@
 //! Access the native system.
-mod action;
-mod information;
+use crate::futures::futures::channel::oneshot;
 
-pub use action::Action;
-pub use information::Information;
+/// An operation to be performed on the system.
+#[derive(Debug)]
+pub enum Action {
+    /// Query system information and produce `T` with the result.
+    QueryInformation(oneshot::Sender<Information>),
+}
+
+/// Contains informations about the system (e.g. system name, processor, memory, graphics adapter).
+#[derive(Clone, Debug)]
+pub struct Information {
+    /// The operating system name
+    pub system_name: Option<String>,
+    /// Operating system kernel version
+    pub system_kernel: Option<String>,
+    /// Long operating system version
+    ///
+    /// Examples:
+    /// - MacOS 10.15 Catalina
+    /// - Windows 10 Pro
+    /// - Ubuntu 20.04 LTS (Focal Fossa)
+    pub system_version: Option<String>,
+    /// Short operating system version number
+    pub system_short_version: Option<String>,
+    /// Detailed processor model information
+    pub cpu_brand: String,
+    /// The number of physical cores on the processor
+    pub cpu_cores: Option<usize>,
+    /// Total RAM size, in bytes
+    pub memory_total: u64,
+    /// Memory used by this process, in bytes
+    pub memory_used: Option<u64>,
+    /// Underlying graphics backend for rendering
+    pub graphics_backend: String,
+    /// Model information for the active graphics adapter
+    pub graphics_adapter: String,
+}

runtime/src/system/action.rs

@@ -1,39 +0,0 @@
-use crate::system;
-
-use iced_futures::MaybeSend;
-use std::fmt;
-
-/// An operation to be performed on the system.
-pub enum Action<T> {
-    /// Query system information and produce `T` with the result.
-    QueryInformation(Box<dyn Closure<T>>),
-}
-
-pub trait Closure<T>: Fn(system::Information) -> T + MaybeSend {}
-
-impl<T, O> Closure<O> for T where T: Fn(system::Information) -> O + MaybeSend {}
-
-impl<T> Action<T> {
-    /// Maps the output of a system [`Action`] using the provided closure.
-    pub fn map<A>(
-        self,
-        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
-    ) -> Action<A>
-    where
-        T: 'static,
-    {
-        match self {
-            Self::QueryInformation(o) => {
-                Action::QueryInformation(Box::new(move |s| f(o(s))))
-            }
-        }
-    }
-}
-
-impl<T> fmt::Debug for Action<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::QueryInformation(_) => write!(f, "Action::QueryInformation"),
-        }
-    }
-}

runtime/src/system/information.rs

@@ -1,29 +0,0 @@
-/// Contains informations about the system (e.g. system name, processor, memory, graphics adapter).
-#[derive(Clone, Debug)]
-pub struct Information {
-    /// The operating system name
-    pub system_name: Option<String>,
-    /// Operating system kernel version
-    pub system_kernel: Option<String>,
-    /// Long operating system version
-    ///
-    /// Examples:
-    /// - MacOS 10.15 Catalina
-    /// - Windows 10 Pro
-    /// - Ubuntu 20.04 LTS (Focal Fossa)
-    pub system_version: Option<String>,
-    /// Short operating system version number
-    pub system_short_version: Option<String>,
-    /// Detailed processor model information
-    pub cpu_brand: String,
-    /// The number of physical cores on the processor
-    pub cpu_cores: Option<usize>,
-    /// Total RAM size, in bytes
-    pub memory_total: u64,
-    /// Memory used by this process, in bytes
-    pub memory_used: Option<u64>,
-    /// Underlying graphics backend for rendering
-    pub graphics_backend: String,
-    /// Model information for the active graphics adapter
-    pub graphics_adapter: String,
-}

runtime/src/task.rs

@@ -0,0 +1,214 @@
+use crate::core::widget;
+use crate::core::MaybeSend;
+use crate::futures::futures::channel::mpsc;
+use crate::futures::futures::channel::oneshot;
+use crate::futures::futures::future::{self, FutureExt};
+use crate::futures::futures::never::Never;
+use crate::futures::futures::stream::{self, Stream, StreamExt};
+use crate::futures::{boxed_stream, BoxStream};
+use crate::Action;
+
+use std::future::Future;
+
+/// A set of concurrent actions to be performed by the iced runtime.
+///
+/// A [`Task`] _may_ produce a bunch of values of type `T`.
+#[allow(missing_debug_implementations)]
+pub struct Task<T>(Option<BoxStream<Action<T>>>);
+
+impl<T> Task<T> {
+    /// Creates a [`Task`] that does nothing.
+    pub fn none() -> Self {
+        Self(None)
+    }
+
+    /// Creates a new [`Task`] that instantly produces the given value.
+    pub fn done(value: T) -> Self
+    where
+        T: MaybeSend + 'static,
+    {
+        Self::future(future::ready(value))
+    }
+
+    /// Creates a new [`Task`] that runs the given [`Future`] and produces
+    /// its output.
+    pub fn future(future: impl Future<Output = T> + MaybeSend + 'static) -> Self
+    where
+        T: 'static,
+    {
+        Self::stream(stream::once(future))
+    }
+
+    /// Creates a new [`Task`] that runs the given [`Stream`] and produces
+    /// each of its items.
+    pub fn stream(stream: impl Stream<Item = T> + MaybeSend + 'static) -> Self
+    where
+        T: 'static,
+    {
+        Self(Some(boxed_stream(stream.map(Action::Output))))
+    }
+
+    /// Creates a new [`Task`] that runs the given [`widget::Operation`] and produces
+    /// its output.
+    pub fn widget(operation: impl widget::Operation<T> + 'static) -> Task<T>
+    where
+        T: MaybeSend + 'static,
+    {
+        Self::channel(move |sender| {
+            let operation =
+                widget::operation::map(Box::new(operation), move |value| {
+                    let _ = sender.clone().try_send(value);
+                });
+
+            Action::Widget(Box::new(operation))
+        })
+    }
+
+    /// Creates a new [`Task`] that executes the [`Action`] returned by the closure and
+    /// produces the value fed to the [`oneshot::Sender`].
+    pub fn oneshot(f: impl FnOnce(oneshot::Sender<T>) -> Action<T>) -> Task<T>
+    where
+        T: MaybeSend + 'static,
+    {
+        let (sender, receiver) = oneshot::channel();
+
+        let action = f(sender);
+
+        Self(Some(boxed_stream(
+            stream::once(async move { action }).chain(
+                receiver.into_stream().filter_map(|result| async move {
+                    Some(Action::Output(result.ok()?))
+                }),
+            ),
+        )))
+    }
+
+    /// Creates a new [`Task`] that executes the [`Action`] returned by the closure and
+    /// produces the values fed to the [`mpsc::Sender`].
+    pub fn channel(f: impl FnOnce(mpsc::Sender<T>) -> Action<T>) -> Task<T>
+    where
+        T: MaybeSend + 'static,
+    {
+        let (sender, receiver) = mpsc::channel(1);
+
+        let action = f(sender);
+
+        Self(Some(boxed_stream(
+            stream::once(async move { action })
+                .chain(receiver.map(|result| Action::Output(result))),
+        )))
+    }
+
+    /// Creates a new [`Task`] that executes the given [`Action`] and produces no output.
+    pub fn effect(action: impl Into<Action<Never>>) -> Self {
+        let action = action.into();
+
+        Self(Some(boxed_stream(stream::once(async move {
+            action.output().expect_err("no output")
+        }))))
+    }
+
+    /// Maps the output of a [`Task`] with the given closure.
+    pub fn map<O>(
+        self,
+        mut f: impl FnMut(T) -> O + MaybeSend + 'static,
+    ) -> Task<O>
+    where
+        T: MaybeSend + 'static,
+        O: MaybeSend + 'static,
+    {
+        self.then(move |output| Task::done(f(output)))
+    }
+
+    /// Performs a new [`Task`] for every output of the current [`Task`] using the
+    /// given closure.
+    ///
+    /// This is the monadic interface of [`Task`]—analogous to [`Future`] and
+    /// [`Stream`].
+    pub fn then<O>(
+        self,
+        mut f: impl FnMut(T) -> Task<O> + MaybeSend + 'static,
+    ) -> Task<O>
+    where
+        T: MaybeSend + 'static,
+        O: MaybeSend + 'static,
+    {
+        Task(match self.0 {
+            None => None,
+            Some(stream) => {
+                Some(boxed_stream(stream.flat_map(move |action| {
+                    match action.output() {
+                        Ok(output) => f(output)
+                            .0
+                            .unwrap_or_else(|| boxed_stream(stream::empty())),
+                        Err(action) => {
+                            boxed_stream(stream::once(async move { action }))
+                        }
+                    }
+                })))
+            }
+        })
+    }
+
+    /// Chains a new [`Task`] to be performed once the current one finishes completely.
+    pub fn chain(self, task: Self) -> Self
+    where
+        T: 'static,
+    {
+        match self.0 {
+            None => task,
+            Some(first) => match task.0 {
+                None => Task::none(),
+                Some(second) => Task(Some(boxed_stream(first.chain(second)))),
+            },
+        }
+    }
+
+    /// Creates a [`Task`] that runs the given [`Future`] to completion.
+    pub fn perform<A>(
+        future: impl Future<Output = A> + MaybeSend + 'static,
+        f: impl Fn(A) -> T + MaybeSend + 'static,
+    ) -> Self
+    where
+        T: MaybeSend + 'static,
+        A: MaybeSend + 'static,
+    {
+        Self::future(future.map(f))
+    }
+
+    /// Creates a [`Task`] that runs the given [`Stream`] to completion.
+    pub fn run<A>(
+        stream: impl Stream<Item = A> + MaybeSend + 'static,
+        f: impl Fn(A) -> T + 'static + MaybeSend,
+    ) -> Self
+    where
+        T: 'static,
+    {
+        Self::stream(stream.map(f))
+    }
+
+    /// Combines the given tasks and produces a single [`Task`] that will run all of them
+    /// in parallel.
+    pub fn batch(tasks: impl IntoIterator<Item = Self>) -> Self
+    where
+        T: 'static,
+    {
+        Self(Some(boxed_stream(stream::select_all(
+            tasks.into_iter().filter_map(|task| task.0),
+        ))))
+    }
+
+    /// Returns the underlying [`Stream`] of the [`Task`].
+    pub fn into_stream(self) -> Option<BoxStream<Action<T>>> {
+        self.0
+    }
+}
+
+impl<T> From<()> for Task<T>
+where
+    T: MaybeSend + 'static,
+{
+    fn from(_value: ()) -> Self {
+        Self::none()
+    }
+}

runtime/src/user_interface.rs

@@ -566,7 +566,7 @@ where
     pub fn operate(
         &mut self,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         self.root.as_widget().operate(
             &mut self.state,

runtime/src/window.rs

@@ -1,24 +1,145 @@
 //! Build window-based GUI applications.
-mod action;
-
 pub mod screenshot;
 
-pub use action::Action;
 pub use screenshot::Screenshot;
 
-use crate::command::{self, Command};
 use crate::core::time::Instant;
 use crate::core::window::{
     Event, Icon, Id, Level, Mode, Settings, UserAttention,
 };
-use crate::core::{Point, Size};
+use crate::core::{MaybeSend, Point, Size};
 use crate::futures::event;
+use crate::futures::futures::channel::oneshot;
 use crate::futures::Subscription;
+use crate::Task;
 
 pub use raw_window_handle;
 
 use raw_window_handle::WindowHandle;
 
+/// An operation to be performed on some window.
+#[allow(missing_debug_implementations)]
+pub enum Action {
+    /// Opens a new window with some [`Settings`].
+    Open(Id, Settings),
+
+    /// Close the window and exits the application.
+    Close(Id),
+
+    /// Move the window with the left mouse button until the button is
+    /// released.
+    ///
+    /// There’s no guarantee that this will work unless the left mouse
+    /// button was pressed immediately before this function is called.
+    Drag(Id),
+
+    /// Resize the window to the given logical dimensions.
+    Resize(Id, Size),
+
+    /// Fetch the current logical dimensions of the window.
+    FetchSize(Id, oneshot::Sender<Size>),
+
+    /// Fetch if the current window is maximized or not.
+    FetchMaximized(Id, oneshot::Sender<bool>),
+
+    /// Set the window to maximized or back
+    Maximize(Id, bool),
+
+    /// Fetch if the current window is minimized or not.
+    ///
+    /// ## Platform-specific
+    /// - **Wayland:** Always `None`.
+    FetchMinimized(Id, oneshot::Sender<Option<bool>>),
+
+    /// Set the window to minimized or back
+    Minimize(Id, bool),
+
+    /// Fetch the current logical coordinates of the window.
+    FetchPosition(Id, oneshot::Sender<Option<Point>>),
+
+    /// Move the window to the given logical coordinates.
+    ///
+    /// Unsupported on Wayland.
+    Move(Id, Point),
+
+    /// Change the [`Mode`] of the window.
+    ChangeMode(Id, Mode),
+
+    /// Fetch the current [`Mode`] of the window.
+    FetchMode(Id, oneshot::Sender<Mode>),
+
+    /// Toggle the window to maximized or back
+    ToggleMaximize(Id),
+
+    /// Toggle whether window has decorations.
+    ///
+    /// ## Platform-specific
+    /// - **X11:** Not implemented.
+    /// - **Web:** Unsupported.
+    ToggleDecorations(Id),
+
+    /// Request user attention to the window, this has no effect if the application
+    /// is already focused. How requesting for user attention manifests is platform dependent,
+    /// see [`UserAttention`] for details.
+    ///
+    /// Providing `None` will unset the request for user attention. Unsetting the request for
+    /// user attention might not be done automatically by the WM when the window receives input.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **iOS / Android / Web:** Unsupported.
+    /// - **macOS:** `None` has no effect.
+    /// - **X11:** Requests for user attention must be manually cleared.
+    /// - **Wayland:** Requires `xdg_activation_v1` protocol, `None` has no effect.
+    RequestUserAttention(Id, Option<UserAttention>),
+
+    /// Bring the window to the front and sets input focus. Has no effect if the window is
+    /// already in focus, minimized, or not visible.
+    ///
+    /// This method steals input focus from other applications. Do not use this method unless
+    /// you are certain that's what the user wants. Focus stealing can cause an extremely disruptive
+    /// user experience.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Web / Wayland:** Unsupported.
+    GainFocus(Id),
+
+    /// Change the window [`Level`].
+    ChangeLevel(Id, Level),
+
+    /// Show the system menu at cursor position.
+    ///
+    /// ## Platform-specific
+    /// Android / iOS / macOS / Orbital / Web / X11: Unsupported.
+    ShowSystemMenu(Id),
+
+    /// Fetch the raw identifier unique to the window.
+    FetchRawId(Id, oneshot::Sender<u64>),
+
+    /// Change the window [`Icon`].
+    ///
+    /// On Windows and X11, this is typically the small icon in the top-left
+    /// corner of the titlebar.
+    ///
+    /// ## Platform-specific
+    ///
+    /// - **Web / Wayland / macOS:** Unsupported.
+    ///
+    /// - **Windows:** Sets `ICON_SMALL`. The base size for a window icon is 16x16, but it's
+    ///   recommended to account for screen scaling and pick a multiple of that, i.e. 32x32.
+    ///
+    /// - **X11:** Has no universal guidelines for icon sizes, so you're at the whims of the WM. That
+    ///   said, it's usually in the same ballpark as on Windows.
+    ChangeIcon(Id, Icon),
+
+    /// Runs the closure with the native window handle of the window with the given [`Id`].
+    RunWithHandle(Id, Box<dyn FnOnce(WindowHandle<'_>) + Send>),
+
+    /// Screenshot the viewport of the window.
+    Screenshot(Id, oneshot::Sender<Screenshot>),
+}
+
 /// Subscribes to the frames of the window of the running application.
 ///
 /// The resulting [`Subscription`] will produce items at a rate equal to the
@@ -34,110 +155,96 @@ pub fn frames() -> Subscription<Instant> {
     })
 }
 
-/// Spawns a new window with the given `settings`.
+/// Opens a new window with the given `settings`.
 ///
-/// Returns the new window [`Id`] alongside the [`Command`].
-pub fn spawn<Message>(settings: Settings) -> (Id, Command<Message>) {
+/// Returns the new window [`Id`] alongside the [`Task`].
+pub fn open<T>(settings: Settings) -> (Id, Task<T>) {
     let id = Id::unique();
 
     (
         id,
-        Command::single(command::Action::Window(Action::Spawn(id, settings))),
+        Task::effect(crate::Action::Window(Action::Open(id, settings))),
     )
 }
 
 /// Closes the window with `id`.
-pub fn close<Message>(id: Id) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Close(id)))
+pub fn close<T>(id: Id) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::Close(id)))
 }
 
 /// Begins dragging the window while the left mouse button is held.
-pub fn drag<Message>(id: Id) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Drag(id)))
+pub fn drag<T>(id: Id) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::Drag(id)))
 }
 
 /// Resizes the window to the given logical dimensions.
-pub fn resize<Message>(id: Id, new_size: Size) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Resize(id, new_size)))
+pub fn resize<T>(id: Id, new_size: Size) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::Resize(id, new_size)))
 }
 
 /// Fetches the window's size in logical dimensions.
-pub fn fetch_size<Message>(
-    id: Id,
-    f: impl FnOnce(Size) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchSize(id, Box::new(f))))
+pub fn fetch_size(id: Id) -> Task<Size> {
+    Task::oneshot(move |channel| {
+        crate::Action::Window(Action::FetchSize(id, channel))
+    })
 }
 
 /// Fetches if the window is maximized.
-pub fn fetch_maximized<Message>(
-    id: Id,
-    f: impl FnOnce(bool) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchMaximized(
-        id,
-        Box::new(f),
-    )))
+pub fn fetch_maximized(id: Id) -> Task<bool> {
+    Task::oneshot(move |channel| {
+        crate::Action::Window(Action::FetchMaximized(id, channel))
+    })
 }
 
 /// Maximizes the window.
-pub fn maximize<Message>(id: Id, maximized: bool) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Maximize(id, maximized)))
+pub fn maximize<T>(id: Id, maximized: bool) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::Maximize(id, maximized)))
 }
 
 /// Fetches if the window is minimized.
-pub fn fetch_minimized<Message>(
-    id: Id,
-    f: impl FnOnce(Option<bool>) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchMinimized(
-        id,
-        Box::new(f),
-    )))
+pub fn fetch_minimized(id: Id) -> Task<Option<bool>> {
+    Task::oneshot(move |channel| {
+        crate::Action::Window(Action::FetchMinimized(id, channel))
+    })
 }
 
 /// Minimizes the window.
-pub fn minimize<Message>(id: Id, minimized: bool) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Minimize(id, minimized)))
+pub fn minimize<T>(id: Id, minimized: bool) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::Minimize(id, minimized)))
 }
 
 /// Fetches the current window position in logical coordinates.
-pub fn fetch_position<Message>(
-    id: Id,
-    f: impl FnOnce(Option<Point>) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchPosition(
-        id,
-        Box::new(f),
-    )))
+pub fn fetch_position(id: Id) -> Task<Option<Point>> {
+    Task::oneshot(move |channel| {
+        crate::Action::Window(Action::FetchPosition(id, channel))
+    })
 }
 
 /// Moves the window to the given logical coordinates.
-pub fn move_to<Message>(id: Id, position: Point) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Move(id, position)))
+pub fn move_to<T>(id: Id, position: Point) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::Move(id, position)))
 }
 
 /// Changes the [`Mode`] of the window.
-pub fn change_mode<Message>(id: Id, mode: Mode) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ChangeMode(id, mode)))
+pub fn change_mode<T>(id: Id, mode: Mode) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::ChangeMode(id, mode)))
 }
 
 /// Fetches the current [`Mode`] of the window.
-pub fn fetch_mode<Message>(
-    id: Id,
-    f: impl FnOnce(Mode) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchMode(id, Box::new(f))))
+pub fn fetch_mode(id: Id) -> Task<Mode> {
+    Task::oneshot(move |channel| {
+        crate::Action::Window(Action::FetchMode(id, channel))
+    })
 }
 
 /// Toggles the window to maximized or back.
-pub fn toggle_maximize<Message>(id: Id) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ToggleMaximize(id)))
+pub fn toggle_maximize<T>(id: Id) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::ToggleMaximize(id)))
 }
 
 /// Toggles the window decorations.
-pub fn toggle_decorations<Message>(id: Id) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ToggleDecorations(id)))
+pub fn toggle_decorations<T>(id: Id) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::ToggleDecorations(id)))
 }
 
 /// Request user attention to the window. This has no effect if the application
@@ -146,11 +253,11 @@ pub fn toggle_decorations<Message>(id: Id) -> Command<Message> {
 ///
 /// Providing `None` will unset the request for user attention. Unsetting the request for
 /// user attention might not be done automatically by the WM when the window receives input.
-pub fn request_user_attention<Message>(
+pub fn request_user_attention<T>(
     id: Id,
     user_attention: Option<UserAttention>,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::RequestUserAttention(
+) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::RequestUserAttention(
         id,
         user_attention,
     )))
@@ -159,59 +266,61 @@ pub fn request_user_attention<Message>(
 /// Brings the window to the front and sets input focus. Has no effect if the window is
 /// already in focus, minimized, or not visible.
 ///
-/// This [`Command`] steals input focus from other applications. Do not use this method unless
+/// This [`Task`] steals input focus from other applications. Do not use this method unless
 /// you are certain that's what the user wants. Focus stealing can cause an extremely disruptive
 /// user experience.
-pub fn gain_focus<Message>(id: Id) -> Command<Message> {
-    Command::single(command::Action::Window(Action::GainFocus(id)))
+pub fn gain_focus<T>(id: Id) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::GainFocus(id)))
 }
 
 /// Changes the window [`Level`].
-pub fn change_level<Message>(id: Id, level: Level) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ChangeLevel(id, level)))
+pub fn change_level<T>(id: Id, level: Level) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::ChangeLevel(id, level)))
 }
 
 /// Show the [system menu] at cursor position.
 ///
 /// [system menu]: https://en.wikipedia.org/wiki/Common_menus_in_Microsoft_Windows#System_menu
-pub fn show_system_menu<Message>(id: Id) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ShowSystemMenu(id)))
+pub fn show_system_menu<T>(id: Id) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::ShowSystemMenu(id)))
 }
 
 /// Fetches an identifier unique to the window, provided by the underlying windowing system. This is
 /// not to be confused with [`Id`].
-pub fn fetch_id<Message>(
-    id: Id,
-    f: impl FnOnce(u64) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::FetchId(id, Box::new(f))))
+pub fn fetch_raw_id<Message>(id: Id) -> Task<u64> {
+    Task::oneshot(|channel| {
+        crate::Action::Window(Action::FetchRawId(id, channel))
+    })
 }
 
 /// Changes the [`Icon`] of the window.
-pub fn change_icon<Message>(id: Id, icon: Icon) -> Command<Message> {
-    Command::single(command::Action::Window(Action::ChangeIcon(id, icon)))
+pub fn change_icon<T>(id: Id, icon: Icon) -> Task<T> {
+    Task::effect(crate::Action::Window(Action::ChangeIcon(id, icon)))
 }
 
 /// Runs the given callback with the native window handle for the window with the given id.
 ///
 /// Note that if the window closes before this call is processed the callback will not be run.
-pub fn run_with_handle<Message>(
+pub fn run_with_handle<T>(
     id: Id,
-    f: impl FnOnce(WindowHandle<'_>) -> Message + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::RunWithHandle(
+    f: impl FnOnce(WindowHandle<'_>) -> T + MaybeSend + 'static,
+) -> Task<T>
+where
+    T: MaybeSend + 'static,
+{
+    Task::oneshot(move |channel| {
+        crate::Action::Window(Action::RunWithHandle(
             id,
-        Box::new(f),
-    )))
+            Box::new(move |handle| {
+                let _ = channel.send(f(handle));
+            }),
+        ))
+    })
 }
 
 /// Captures a [`Screenshot`] from the window.
-pub fn screenshot<Message>(
-    id: Id,
-    f: impl FnOnce(Screenshot) -> Message + Send + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::Window(Action::Screenshot(
-        id,
-        Box::new(f),
-    )))
+pub fn screenshot(id: Id) -> Task<Screenshot> {
+    Task::oneshot(move |channel| {
+        crate::Action::Window(Action::Screenshot(id, channel))
+    })
 }

runtime/src/window/action.rs

@@ -1,230 +0,0 @@
-use crate::core::window::{Icon, Id, Level, Mode, Settings, UserAttention};
-use crate::core::{Point, Size};
-use crate::futures::MaybeSend;
-use crate::window::Screenshot;
-
-use raw_window_handle::WindowHandle;
-
-use std::fmt;
-
-/// An operation to be performed on some window.
-pub enum Action<T> {
-    /// Spawns a new window with some [`Settings`].
-    Spawn(Id, Settings),
-    /// Close the window and exits the application.
-    Close(Id),
-    /// Move the window with the left mouse button until the button is
-    /// released.
-    ///
-    /// There’s no guarantee that this will work unless the left mouse
-    /// button was pressed immediately before this function is called.
-    Drag(Id),
-    /// Resize the window to the given logical dimensions.
-    Resize(Id, Size),
-    /// Fetch the current logical dimensions of the window.
-    FetchSize(Id, Box<dyn FnOnce(Size) -> T + 'static>),
-    /// Fetch if the current window is maximized or not.
-    ///
-    /// ## Platform-specific
-    /// - **iOS / Android / Web:** Unsupported.
-    FetchMaximized(Id, Box<dyn FnOnce(bool) -> T + 'static>),
-    /// Set the window to maximized or back
-    Maximize(Id, bool),
-    /// Fetch if the current window is minimized or not.
-    ///
-    /// ## Platform-specific
-    /// - **Wayland:** Always `None`.
-    /// - **iOS / Android / Web:** Unsupported.
-    FetchMinimized(Id, Box<dyn FnOnce(Option<bool>) -> T + 'static>),
-    /// Set the window to minimized or back
-    Minimize(Id, bool),
-    /// Fetch the current logical coordinates of the window.
-    FetchPosition(Id, Box<dyn FnOnce(Option<Point>) -> T + 'static>),
-    /// Move the window to the given logical coordinates.
-    ///
-    /// Unsupported on Wayland.
-    Move(Id, Point),
-    /// Change the [`Mode`] of the window.
-    ChangeMode(Id, Mode),
-    /// Fetch the current [`Mode`] of the window.
-    FetchMode(Id, Box<dyn FnOnce(Mode) -> T + 'static>),
-    /// Toggle the window to maximized or back
-    ToggleMaximize(Id),
-    /// Toggle whether window has decorations.
-    ///
-    /// ## Platform-specific
-    /// - **X11:** Not implemented.
-    /// - **Web:** Unsupported.
-    ToggleDecorations(Id),
-    /// Request user attention to the window, this has no effect if the application
-    /// is already focused. How requesting for user attention manifests is platform dependent,
-    /// see [`UserAttention`] for details.
-    ///
-    /// Providing `None` will unset the request for user attention. Unsetting the request for
-    /// user attention might not be done automatically by the WM when the window receives input.
-    ///
-    /// ## Platform-specific
-    ///
-    /// - **iOS / Android / Web:** Unsupported.
-    /// - **macOS:** `None` has no effect.
-    /// - **X11:** Requests for user attention must be manually cleared.
-    /// - **Wayland:** Requires `xdg_activation_v1` protocol, `None` has no effect.
-    RequestUserAttention(Id, Option<UserAttention>),
-    /// Bring the window to the front and sets input focus. Has no effect if the window is
-    /// already in focus, minimized, or not visible.
-    ///
-    /// This method steals input focus from other applications. Do not use this method unless
-    /// you are certain that's what the user wants. Focus stealing can cause an extremely disruptive
-    /// user experience.
-    ///
-    /// ## Platform-specific
-    ///
-    /// - **Web / Wayland:** Unsupported.
-    GainFocus(Id),
-    /// Change the window [`Level`].
-    ChangeLevel(Id, Level),
-    /// Show the system menu at cursor position.
-    ///
-    /// ## Platform-specific
-    /// Android / iOS / macOS / Orbital / Web / X11: Unsupported.
-    ShowSystemMenu(Id),
-    /// Fetch the raw identifier unique to the window.
-    FetchId(Id, Box<dyn FnOnce(u64) -> T + 'static>),
-    /// Change the window [`Icon`].
-    ///
-    /// On Windows and X11, this is typically the small icon in the top-left
-    /// corner of the titlebar.
-    ///
-    /// ## Platform-specific
-    ///
-    /// - **Web / Wayland / macOS:** Unsupported.
-    ///
-    /// - **Windows:** Sets `ICON_SMALL`. The base size for a window icon is 16x16, but it's
-    ///   recommended to account for screen scaling and pick a multiple of that, i.e. 32x32.
-    ///
-    /// - **X11:** Has no universal guidelines for icon sizes, so you're at the whims of the WM. That
-    ///   said, it's usually in the same ballpark as on Windows.
-    ChangeIcon(Id, Icon),
-    /// Runs the closure with the native window handle of the window with the given [`Id`].
-    RunWithHandle(Id, Box<dyn FnOnce(WindowHandle<'_>) -> T + 'static>),
-    /// Screenshot the viewport of the window.
-    Screenshot(Id, Box<dyn FnOnce(Screenshot) -> T + 'static>),
-}
-
-impl<T> Action<T> {
-    /// Maps the output of a window [`Action`] using the provided closure.
-    pub fn map<A>(
-        self,
-        f: impl Fn(T) -> A + 'static + MaybeSend + Sync,
-    ) -> Action<A>
-    where
-        T: 'static,
-    {
-        match self {
-            Self::Spawn(id, settings) => Action::Spawn(id, settings),
-            Self::Close(id) => Action::Close(id),
-            Self::Drag(id) => Action::Drag(id),
-            Self::Resize(id, size) => Action::Resize(id, size),
-            Self::FetchSize(id, o) => {
-                Action::FetchSize(id, Box::new(move |s| f(o(s))))
-            }
-            Self::FetchMaximized(id, o) => {
-                Action::FetchMaximized(id, Box::new(move |s| f(o(s))))
-            }
-            Self::Maximize(id, maximized) => Action::Maximize(id, maximized),
-            Self::FetchMinimized(id, o) => {
-                Action::FetchMinimized(id, Box::new(move |s| f(o(s))))
-            }
-            Self::Minimize(id, minimized) => Action::Minimize(id, minimized),
-            Self::FetchPosition(id, o) => {
-                Action::FetchPosition(id, Box::new(move |s| f(o(s))))
-            }
-            Self::Move(id, position) => Action::Move(id, position),
-            Self::ChangeMode(id, mode) => Action::ChangeMode(id, mode),
-            Self::FetchMode(id, o) => {
-                Action::FetchMode(id, Box::new(move |s| f(o(s))))
-            }
-            Self::ToggleMaximize(id) => Action::ToggleMaximize(id),
-            Self::ToggleDecorations(id) => Action::ToggleDecorations(id),
-            Self::RequestUserAttention(id, attention_type) => {
-                Action::RequestUserAttention(id, attention_type)
-            }
-            Self::GainFocus(id) => Action::GainFocus(id),
-            Self::ChangeLevel(id, level) => Action::ChangeLevel(id, level),
-            Self::ShowSystemMenu(id) => Action::ShowSystemMenu(id),
-            Self::FetchId(id, o) => {
-                Action::FetchId(id, Box::new(move |s| f(o(s))))
-            }
-            Self::ChangeIcon(id, icon) => Action::ChangeIcon(id, icon),
-            Self::RunWithHandle(id, o) => {
-                Action::RunWithHandle(id, Box::new(move |s| f(o(s))))
-            }
-            Self::Screenshot(id, tag) => Action::Screenshot(
-                id,
-                Box::new(move |screenshot| f(tag(screenshot))),
-            ),
-        }
-    }
-}
-
-impl<T> fmt::Debug for Action<T> {
-    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
-        match self {
-            Self::Spawn(id, settings) => {
-                write!(f, "Action::Spawn({id:?}, {settings:?})")
-            }
-            Self::Close(id) => write!(f, "Action::Close({id:?})"),
-            Self::Drag(id) => write!(f, "Action::Drag({id:?})"),
-            Self::Resize(id, size) => {
-                write!(f, "Action::Resize({id:?}, {size:?})")
-            }
-            Self::FetchSize(id, _) => write!(f, "Action::FetchSize({id:?})"),
-            Self::FetchMaximized(id, _) => {
-                write!(f, "Action::FetchMaximized({id:?})")
-            }
-            Self::Maximize(id, maximized) => {
-                write!(f, "Action::Maximize({id:?}, {maximized})")
-            }
-            Self::FetchMinimized(id, _) => {
-                write!(f, "Action::FetchMinimized({id:?})")
-            }
-            Self::Minimize(id, minimized) => {
-                write!(f, "Action::Minimize({id:?}, {minimized}")
-            }
-            Self::FetchPosition(id, _) => {
-                write!(f, "Action::FetchPosition({id:?})")
-            }
-            Self::Move(id, position) => {
-                write!(f, "Action::Move({id:?}, {position})")
-            }
-            Self::ChangeMode(id, mode) => {
-                write!(f, "Action::SetMode({id:?}, {mode:?})")
-            }
-            Self::FetchMode(id, _) => write!(f, "Action::FetchMode({id:?})"),
-            Self::ToggleMaximize(id) => {
-                write!(f, "Action::ToggleMaximize({id:?})")
-            }
-            Self::ToggleDecorations(id) => {
-                write!(f, "Action::ToggleDecorations({id:?})")
-            }
-            Self::RequestUserAttention(id, _) => {
-                write!(f, "Action::RequestUserAttention({id:?})")
-            }
-            Self::GainFocus(id) => write!(f, "Action::GainFocus({id:?})"),
-            Self::ChangeLevel(id, level) => {
-                write!(f, "Action::ChangeLevel({id:?}, {level:?})")
-            }
-            Self::ShowSystemMenu(id) => {
-                write!(f, "Action::ShowSystemMenu({id:?})")
-            }
-            Self::FetchId(id, _) => write!(f, "Action::FetchId({id:?})"),
-            Self::ChangeIcon(id, _icon) => {
-                write!(f, "Action::ChangeIcon({id:?})")
-            }
-            Self::RunWithHandle(id, _) => {
-                write!(f, "Action::RunWithHandle({id:?})")
-            }
-            Self::Screenshot(id, _) => write!(f, "Action::Screenshot({id:?})"),
-        }
-    }
-}

src/application.rs

@@ -2,7 +2,7 @@
 use crate::core::text;
 use crate::graphics::compositor;
 use crate::shell::application;
-use crate::{Command, Element, Executor, Settings, Subscription};
+use crate::{Element, Executor, Settings, Subscription, Task};
 
 pub use application::{Appearance, DefaultStyle};
 
@@ -16,7 +16,7 @@ pub use application::{Appearance, DefaultStyle};
 ///   document.
 ///
 /// An [`Application`] can execute asynchronous actions by returning a
-/// [`Command`] in some of its methods.
+/// [`Task`] in some of its methods.
 ///
 /// When using an [`Application`] with the `debug` feature enabled, a debug view
 /// can be toggled by pressing `F12`.
@@ -62,7 +62,7 @@ pub use application::{Appearance, DefaultStyle};
 /// ```no_run
 /// use iced::advanced::Application;
 /// use iced::executor;
-/// use iced::{Command, Element, Settings, Theme, Renderer};
+/// use iced::{Task, Element, Settings, Theme, Renderer};
 ///
 /// pub fn main() -> iced::Result {
 ///     Hello::run(Settings::default())
@@ -77,16 +77,16 @@ pub use application::{Appearance, DefaultStyle};
 ///     type Theme = Theme;
 ///     type Renderer = Renderer;
 ///
-///     fn new(_flags: ()) -> (Hello, Command<Self::Message>) {
-///         (Hello, Command::none())
+///     fn new(_flags: ()) -> (Hello, Task<Self::Message>) {
+///         (Hello, Task::none())
 ///     }
 ///
 ///     fn title(&self) -> String {
 ///         String::from("A cool application")
 ///     }
 ///
-///     fn update(&mut self, _message: Self::Message) -> Command<Self::Message> {
-///         Command::none()
+///     fn update(&mut self, _message: Self::Message) -> Task<Self::Message> {
+///         Task::none()
 ///     }
 ///
 ///     fn view(&self) -> Element<Self::Message> {
@@ -123,12 +123,12 @@ where
     ///
     /// Here is where you should return the initial state of your app.
     ///
-    /// Additionally, you can return a [`Command`] if you need to perform some
+    /// Additionally, you can return a [`Task`] if you need to perform some
     /// async action in the background on startup. This is useful if you want to
     /// load state from a file, perform an initial HTTP request, etc.
     ///
     /// [`run`]: Self::run
-    fn new(flags: Self::Flags) -> (Self, Command<Self::Message>);
+    fn new(flags: Self::Flags) -> (Self, Task<Self::Message>);
 
     /// Returns the current title of the [`Application`].
     ///
@@ -142,8 +142,8 @@ where
     /// produced by either user interactions or commands, will be handled by
     /// this method.
     ///
-    /// Any [`Command`] returned will be executed immediately in the background.
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
+    /// Any [`Task`] returned will be executed immediately in the background.
+    fn update(&mut self, message: Self::Message) -> Task<Self::Message>;
 
     /// Returns the widgets to display in the [`Application`].
     ///
@@ -234,7 +234,7 @@ where
     type Theme = A::Theme;
     type Renderer = A::Renderer;
 
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message> {
+    fn update(&mut self, message: Self::Message) -> Task<Self::Message> {
         self.0.update(message)
     }
 
@@ -250,7 +250,7 @@ where
 {
     type Flags = A::Flags;
 
-    fn new(flags: Self::Flags) -> (Self, Command<A::Message>) {
+    fn new(flags: Self::Flags) -> (Self, Task<A::Message>) {
         let (app, command) = A::new(flags);
 
         (Instance(app), command)

src/lib.rs

@@ -203,6 +203,7 @@ pub use crate::core::{
     Length, Padding, Pixels, Point, Radians, Rectangle, Rotation, Shadow, Size,
     Theme, Transformation, Vector,
 };
+pub use crate::runtime::Task;
 
 pub mod clipboard {
     //! Access the clipboard.
@@ -256,11 +257,6 @@ pub mod mouse {
     };
 }
 
-pub mod command {
-    //! Run asynchronous actions.
-    pub use crate::runtime::command::{channel, Command};
-}
-
 pub mod subscription {
     //! Listen to external events in your application.
     pub use iced_futures::subscription::{
@@ -312,7 +308,6 @@ pub mod widget {
     mod runtime {}
 }
 
-pub use command::Command;
 pub use error::Error;
 pub use event::Event;
 pub use executor::Executor;

src/multi_window.rs

@@ -1,6 +1,6 @@
 //! Leverage multi-window support in your application.
 use crate::window;
-use crate::{Command, Element, Executor, Settings, Subscription};
+use crate::{Element, Executor, Settings, Subscription, Task};
 
 pub use crate::application::{Appearance, DefaultStyle};
 
@@ -14,7 +14,7 @@ pub use crate::application::{Appearance, DefaultStyle};
 ///   document and display only the contents of the `window::Id::MAIN` window.
 ///
 /// An [`Application`] can execute asynchronous actions by returning a
-/// [`Command`] in some of its methods.
+/// [`Task`] in some of its methods.
 ///
 /// When using an [`Application`] with the `debug` feature enabled, a debug view
 /// can be toggled by pressing `F12`.
@@ -29,7 +29,7 @@ pub use crate::application::{Appearance, DefaultStyle};
 ///
 /// ```no_run
 /// use iced::{executor, window};
-/// use iced::{Command, Element, Settings, Theme};
+/// use iced::{Task, Element, Settings, Theme};
 /// use iced::multi_window::{self, Application};
 ///
 /// pub fn main() -> iced::Result {
@@ -44,16 +44,16 @@ pub use crate::application::{Appearance, DefaultStyle};
 ///     type Message = ();
 ///     type Theme = Theme;
 ///
-///     fn new(_flags: ()) -> (Hello, Command<Self::Message>) {
-///         (Hello, Command::none())
+///     fn new(_flags: ()) -> (Hello, Task<Self::Message>) {
+///         (Hello, Task::none())
 ///     }
 ///
 ///     fn title(&self, _window: window::Id) -> String {
 ///         String::from("A cool application")
 ///     }
 ///
-///     fn update(&mut self, _message: Self::Message) -> Command<Self::Message> {
-///         Command::none()
+///     fn update(&mut self, _message: Self::Message) -> Task<Self::Message> {
+///         Task::none()
 ///     }
 ///
 ///     fn view(&self, _window: window::Id) -> Element<Self::Message> {
@@ -89,12 +89,12 @@ where
     ///
     /// Here is where you should return the initial state of your app.
     ///
-    /// Additionally, you can return a [`Command`] if you need to perform some
+    /// Additionally, you can return a [`Task`] if you need to perform some
     /// async action in the background on startup. This is useful if you want to
     /// load state from a file, perform an initial HTTP request, etc.
     ///
     /// [`run`]: Self::run
-    fn new(flags: Self::Flags) -> (Self, Command<Self::Message>);
+    fn new(flags: Self::Flags) -> (Self, Task<Self::Message>);
 
     /// Returns the current title of the `window` of the [`Application`].
     ///
@@ -108,8 +108,8 @@ where
     /// produced by either user interactions or commands, will be handled by
     /// this method.
     ///
-    /// Any [`Command`] returned will be executed immediately in the background.
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
+    /// Any [`Task`] returned will be executed immediately in the background.
+    fn update(&mut self, message: Self::Message) -> Task<Self::Message>;
 
     /// Returns the widgets to display in the `window` of the [`Application`].
     ///
@@ -207,7 +207,7 @@ where
     type Theme = A::Theme;
     type Renderer = crate::Renderer;
 
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message> {
+    fn update(&mut self, message: Self::Message) -> Task<Self::Message> {
         self.0.update(message)
     }
 
@@ -226,7 +226,7 @@ where
 {
     type Flags = A::Flags;
 
-    fn new(flags: Self::Flags) -> (Self, Command<A::Message>) {
+    fn new(flags: Self::Flags) -> (Self, Task<A::Message>) {
         let (app, command) = A::new(flags);
 
         (Instance(app), command)

src/program.rs

@@ -35,7 +35,7 @@ use crate::core::text;
 use crate::executor::{self, Executor};
 use crate::graphics::compositor;
 use crate::window;
-use crate::{Command, Element, Font, Result, Settings, Size, Subscription};
+use crate::{Element, Font, Result, Settings, Size, Subscription, Task};
 
 pub use crate::application::{Appearance, DefaultStyle};
 
@@ -76,7 +76,7 @@ pub fn program<State, Message, Theme, Renderer>(
 ) -> Program<impl Definition<State = State, Message = Message, Theme = Theme>>
 where
     State: 'static,
-    Message: Send + std::fmt::Debug,
+    Message: Send + std::fmt::Debug + 'static,
     Theme: Default + DefaultStyle,
     Renderer: self::Renderer,
 {
@@ -94,7 +94,7 @@ where
     impl<State, Message, Theme, Renderer, Update, View> Definition
         for Application<State, Message, Theme, Renderer, Update, View>
     where
-        Message: Send + std::fmt::Debug,
+        Message: Send + std::fmt::Debug + 'static,
         Theme: Default + DefaultStyle,
         Renderer: self::Renderer,
         Update: self::Update<State, Message>,
@@ -106,15 +106,15 @@ where
         type Renderer = Renderer;
         type Executor = executor::Default;
 
-        fn load(&self) -> Command<Self::Message> {
-            Command::none()
+        fn load(&self) -> Task<Self::Message> {
+            Task::none()
         }
 
         fn update(
             &self,
             state: &mut Self::State,
             message: Self::Message,
-        ) -> Command<Self::Message> {
+        ) -> Task<Self::Message> {
             self.update.update(state, message).into()
         }
 
@@ -197,7 +197,7 @@ impl<P: Definition> Program<P> {
 
             fn new(
                 (program, initialize): Self::Flags,
-            ) -> (Self, Command<Self::Message>) {
+            ) -> (Self, Task<Self::Message>) {
                 let state = initialize();
                 let command = program.load();
 
@@ -218,7 +218,7 @@ impl<P: Definition> Program<P> {
             fn update(
                 &mut self,
                 message: Self::Message,
-            ) -> Command<Self::Message> {
+            ) -> Task<Self::Message> {
                 self.program.update(&mut self.state, message)
             }
 
@@ -357,10 +357,10 @@ impl<P: Definition> Program<P> {
         }
     }
 
-    /// Runs the [`Command`] produced by the closure at startup.
+    /// Runs the [`Task`] produced by the closure at startup.
     pub fn load(
         self,
-        f: impl Fn() -> Command<P::Message>,
+        f: impl Fn() -> Task<P::Message>,
     ) -> Program<
         impl Definition<State = P::State, Message = P::Message, Theme = P::Theme>,
     > {
@@ -420,7 +420,7 @@ pub trait Definition: Sized {
     type State;
 
     /// The message of the program.
-    type Message: Send + std::fmt::Debug;
+    type Message: Send + std::fmt::Debug + 'static;
 
     /// The theme of the program.
     type Theme: Default + DefaultStyle;
@@ -431,13 +431,13 @@ pub trait Definition: Sized {
     /// The executor of the program.
     type Executor: Executor;
 
-    fn load(&self) -> Command<Self::Message>;
+    fn load(&self) -> Task<Self::Message>;
 
     fn update(
         &self,
         state: &mut Self::State,
         message: Self::Message,
-    ) -> Command<Self::Message>;
+    ) -> Task<Self::Message>;
 
     fn view<'a>(
         &self,
@@ -484,7 +484,7 @@ fn with_title<P: Definition>(
         type Renderer = P::Renderer;
         type Executor = P::Executor;
 
-        fn load(&self) -> Command<Self::Message> {
+        fn load(&self) -> Task<Self::Message> {
             self.program.load()
         }
 
@@ -496,7 +496,7 @@ fn with_title<P: Definition>(
             &self,
             state: &mut Self::State,
             message: Self::Message,
-        ) -> Command<Self::Message> {
+        ) -> Task<Self::Message> {
             self.program.update(state, message)
         }
 
@@ -532,7 +532,7 @@ fn with_title<P: Definition>(
 
 fn with_load<P: Definition>(
     program: P,
-    f: impl Fn() -> Command<P::Message>,
+    f: impl Fn() -> Task<P::Message>,
 ) -> impl Definition<State = P::State, Message = P::Message, Theme = P::Theme> {
     struct WithLoad<P, F> {
         program: P,
@@ -541,7 +541,7 @@ fn with_load<P: Definition>(
 
     impl<P: Definition, F> Definition for WithLoad<P, F>
     where
-        F: Fn() -> Command<P::Message>,
+        F: Fn() -> Task<P::Message>,
     {
         type State = P::State;
         type Message = P::Message;
@@ -549,15 +549,15 @@ fn with_load<P: Definition>(
         type Renderer = P::Renderer;
         type Executor = executor::Default;
 
-        fn load(&self) -> Command<Self::Message> {
-            Command::batch([self.program.load(), (self.load)()])
+        fn load(&self) -> Task<Self::Message> {
+            Task::batch([self.program.load(), (self.load)()])
         }
 
         fn update(
             &self,
             state: &mut Self::State,
             message: Self::Message,
-        ) -> Command<Self::Message> {
+        ) -> Task<Self::Message> {
             self.program.update(state, message)
         }
 
@@ -621,7 +621,7 @@ fn with_subscription<P: Definition>(
             (self.subscription)(state)
         }
 
-        fn load(&self) -> Command<Self::Message> {
+        fn load(&self) -> Task<Self::Message> {
             self.program.load()
         }
 
@@ -629,7 +629,7 @@ fn with_subscription<P: Definition>(
             &self,
             state: &mut Self::State,
             message: Self::Message,
-        ) -> Command<Self::Message> {
+        ) -> Task<Self::Message> {
             self.program.update(state, message)
         }
 
@@ -686,7 +686,7 @@ fn with_theme<P: Definition>(
             (self.theme)(state)
         }
 
-        fn load(&self) -> Command<Self::Message> {
+        fn load(&self) -> Task<Self::Message> {
             self.program.load()
         }
 
@@ -698,7 +698,7 @@ fn with_theme<P: Definition>(
             &self,
             state: &mut Self::State,
             message: Self::Message,
-        ) -> Command<Self::Message> {
+        ) -> Task<Self::Message> {
             self.program.update(state, message)
         }
 
@@ -755,7 +755,7 @@ fn with_style<P: Definition>(
             (self.style)(state, theme)
         }
 
-        fn load(&self) -> Command<Self::Message> {
+        fn load(&self) -> Task<Self::Message> {
             self.program.load()
         }
 
@@ -767,7 +767,7 @@ fn with_style<P: Definition>(
             &self,
             state: &mut Self::State,
             message: Self::Message,
-        ) -> Command<Self::Message> {
+        ) -> Task<Self::Message> {
             self.program.update(state, message)
         }
 
@@ -822,26 +822,26 @@ where
 /// The update logic of some [`Program`].
 ///
 /// This trait allows the [`program`] builder to take any closure that
-/// returns any `Into<Command<Message>>`.
+/// returns any `Into<Task<Message>>`.
 pub trait Update<State, Message> {
     /// Processes the message and updates the state of the [`Program`].
     fn update(
         &self,
         state: &mut State,
         message: Message,
-    ) -> impl Into<Command<Message>>;
+    ) -> impl Into<Task<Message>>;
 }
 
 impl<T, State, Message, C> Update<State, Message> for T
 where
     T: Fn(&mut State, Message) -> C,
-    C: Into<Command<Message>>,
+    C: Into<Task<Message>>,
 {
     fn update(
         &self,
         state: &mut State,
         message: Message,
-    ) -> impl Into<Command<Message>> {
+    ) -> impl Into<Task<Message>> {
         self(state, message)
     }
 }

widget/src/button.rs

@@ -205,7 +205,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         operation.container(None, layout.bounds(), &mut |operation| {
             self.content.as_widget().operate(

widget/src/column.rs

@@ -208,7 +208,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         operation.container(None, layout.bounds(), &mut |operation| {
             self.children

widget/src/container.rs

@@ -13,7 +13,7 @@ use crate::core::{
     Padding, Pixels, Point, Rectangle, Shadow, Shell, Size, Theme, Vector,
     Widget,
 };
-use crate::runtime::Command;
+use crate::runtime::Task;
 
 /// An element decorating some content.
 ///
@@ -258,7 +258,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         operation.container(
             self.id.as_ref().map(|id| &id.0),
@@ -457,9 +457,9 @@ impl From<Id> for widget::Id {
     }
 }
 
-/// Produces a [`Command`] that queries the visible screen bounds of the
+/// Produces a [`Task`] that queries the visible screen bounds of the
 /// [`Container`] with the given [`Id`].
-pub fn visible_bounds(id: Id) -> Command<Option<Rectangle>> {
+pub fn visible_bounds(id: Id) -> Task<Option<Rectangle>> {
     struct VisibleBounds {
         target: widget::Id,
         depth: usize,
@@ -538,7 +538,7 @@ pub fn visible_bounds(id: Id) -> Command<Option<Rectangle>> {
         }
     }
 
-    Command::widget(VisibleBounds {
+    Task::widget(VisibleBounds {
         target: id.into(),
         depth: 0,
         scrollables: Vec::new(),

widget/src/helpers.rs

@@ -12,7 +12,7 @@ use crate::pick_list::{self, PickList};
 use crate::progress_bar::{self, ProgressBar};
 use crate::radio::{self, Radio};
 use crate::rule::{self, Rule};
-use crate::runtime::Command;
+use crate::runtime::{Action, Task};
 use crate::scrollable::{self, Scrollable};
 use crate::slider::{self, Slider};
 use crate::text::{self, Text};
@@ -275,7 +275,7 @@ where
             state: &mut Tree,
             layout: Layout<'_>,
             renderer: &Renderer,
-            operation: &mut dyn operation::Operation<Message>,
+            operation: &mut dyn operation::Operation<()>,
         ) {
             self.content
                 .as_widget()
@@ -477,7 +477,7 @@ where
             tree: &mut Tree,
             layout: Layout<'_>,
             renderer: &Renderer,
-            operation: &mut dyn operation::Operation<Message>,
+            operation: &mut dyn operation::Operation<()>,
         ) {
             let children = [&self.base, &self.top]
                 .into_iter()
@@ -929,19 +929,13 @@ where
 }
 
 /// Focuses the previous focusable widget.
-pub fn focus_previous<Message>() -> Command<Message>
-where
-    Message: 'static,
-{
-    Command::widget(operation::focusable::focus_previous())
+pub fn focus_previous<T>() -> Task<T> {
+    Task::effect(Action::widget(operation::focusable::focus_previous()))
 }
 
 /// Focuses the next focusable widget.
-pub fn focus_next<Message>() -> Command<Message>
-where
-    Message: 'static,
-{
-    Command::widget(operation::focusable::focus_next())
+pub fn focus_next<T>() -> Task<T> {
+    Task::effect(Action::widget(operation::focusable::focus_next()))
 }
 
 /// A container intercepting mouse events.

widget/src/keyed/column.rs

@@ -265,7 +265,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         operation.container(None, layout.bounds(), &mut |operation| {
             self.children

widget/src/lazy.rs

@@ -182,7 +182,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         self.with_element(|element| {
             element.as_widget().operate(

widget/src/lazy/component.rs

@@ -59,7 +59,7 @@ pub trait Component<Message, Theme = crate::Theme, Renderer = crate::Renderer> {
     fn operate(
         &self,
         _state: &mut Self::State,
-        _operation: &mut dyn widget::Operation<Message>,
+        _operation: &mut dyn widget::Operation<()>,
     ) {
     }
 
@@ -172,7 +172,7 @@ where
 
     fn rebuild_element_with_operation(
         &self,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         let heads = self.state.borrow_mut().take().unwrap().into_heads();
 
@@ -358,70 +358,17 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         self.rebuild_element_with_operation(operation);
 
-        struct MapOperation<'a, B> {
-            operation: &'a mut dyn widget::Operation<B>,
-        }
-
-        impl<'a, T, B> widget::Operation<T> for MapOperation<'a, B> {
-            fn container(
-                &mut self,
-                id: Option<&widget::Id>,
-                bounds: Rectangle,
-                operate_on_children: &mut dyn FnMut(
-                    &mut dyn widget::Operation<T>,
-                ),
-            ) {
-                self.operation.container(id, bounds, &mut |operation| {
-                    operate_on_children(&mut MapOperation { operation });
-                });
-            }
-
-            fn focusable(
-                &mut self,
-                state: &mut dyn widget::operation::Focusable,
-                id: Option<&widget::Id>,
-            ) {
-                self.operation.focusable(state, id);
-            }
-
-            fn text_input(
-                &mut self,
-                state: &mut dyn widget::operation::TextInput,
-                id: Option<&widget::Id>,
-            ) {
-                self.operation.text_input(state, id);
-            }
-
-            fn scrollable(
-                &mut self,
-                state: &mut dyn widget::operation::Scrollable,
-                id: Option<&widget::Id>,
-                bounds: Rectangle,
-                translation: Vector,
-            ) {
-                self.operation.scrollable(state, id, bounds, translation);
-            }
-
-            fn custom(
-                &mut self,
-                state: &mut dyn std::any::Any,
-                id: Option<&widget::Id>,
-            ) {
-                self.operation.custom(state, id);
-            }
-        }
-
         let tree = tree.state.downcast_mut::<Rc<RefCell<Option<Tree>>>>();
         self.with_element(|element| {
             element.as_widget().operate(
                 &mut tree.borrow_mut().as_mut().unwrap().children[0],
                 layout,
                 renderer,
-                &mut MapOperation { operation },
+                operation,
             );
         });
     }

widget/src/lazy/responsive.rs

@@ -161,7 +161,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         let state = tree.state.downcast_mut::<State>();
         let mut content = self.content.borrow_mut();

widget/src/mouse_area.rs

@@ -178,7 +178,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         self.content.as_widget().operate(
             &mut tree.children[0],

widget/src/pane_grid.rs

@@ -324,7 +324,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         operation.container(None, layout.bounds(), &mut |operation| {
             self.contents

widget/src/pane_grid/content.rs

@@ -214,7 +214,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         let body_layout = if let Some(title_bar) = &self.title_bar {
             let mut children = layout.children();

widget/src/pane_grid/title_bar.rs

@@ -278,7 +278,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn widget::Operation<Message>,
+        operation: &mut dyn widget::Operation<()>,
     ) {
         let mut children = layout.children();
         let padded = children.next().unwrap();

widget/src/row.rs

@@ -197,7 +197,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         operation.container(None, layout.bounds(), &mut |operation| {
             self.children

widget/src/scrollable.rs

@@ -15,7 +15,7 @@ use crate::core::{
     self, Background, Border, Clipboard, Color, Element, Layout, Length,
     Pixels, Point, Rectangle, Shell, Size, Theme, Vector, Widget,
 };
-use crate::runtime::Command;
+use crate::runtime::{Action, Task};
 
 pub use operation::scrollable::{AbsoluteOffset, RelativeOffset};
 
@@ -295,7 +295,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         let state = tree.state.downcast_mut::<State>();
 
@@ -952,22 +952,18 @@ impl From<Id> for widget::Id {
     }
 }
 
-/// Produces a [`Command`] that snaps the [`Scrollable`] with the given [`Id`]
+/// Produces a [`Task`] that snaps the [`Scrollable`] with the given [`Id`]
 /// to the provided `percentage` along the x & y axis.
-pub fn snap_to<Message: 'static>(
-    id: Id,
-    offset: RelativeOffset,
-) -> Command<Message> {
-    Command::widget(operation::scrollable::snap_to(id.0, offset))
+pub fn snap_to<T>(id: Id, offset: RelativeOffset) -> Task<T> {
+    Task::effect(Action::widget(operation::scrollable::snap_to(id.0, offset)))
 }
 
-/// Produces a [`Command`] that scrolls the [`Scrollable`] with the given [`Id`]
+/// Produces a [`Task`] that scrolls the [`Scrollable`] with the given [`Id`]
 /// to the provided [`AbsoluteOffset`] along the x & y axis.
-pub fn scroll_to<Message: 'static>(
-    id: Id,
-    offset: AbsoluteOffset,
-) -> Command<Message> {
-    Command::widget(operation::scrollable::scroll_to(id.0, offset))
+pub fn scroll_to<T>(id: Id, offset: AbsoluteOffset) -> Task<T> {
+    Task::effect(Action::widget(operation::scrollable::scroll_to(
+        id.0, offset,
+    )))
 }
 
 /// Returns [`true`] if the viewport actually changed.

widget/src/stack.rs

@@ -189,7 +189,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         operation.container(None, layout.bounds(), &mut |operation| {
             self.children

widget/src/text_input.rs

@@ -30,7 +30,7 @@ use crate::core::{
     Background, Border, Color, Element, Layout, Length, Padding, Pixels, Point,
     Rectangle, Shell, Size, Theme, Vector, Widget,
 };
-use crate::runtime::Command;
+use crate::runtime::{Action, Task};
 
 /// A field that can be filled with text.
 ///
@@ -540,7 +540,7 @@ where
         tree: &mut Tree,
         _layout: Layout<'_>,
         _renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         let state = tree.state.downcast_mut::<State<Renderer::Paragraph>>();
 
@@ -1140,35 +1140,38 @@ impl From<Id> for widget::Id {
     }
 }
 
-/// Produces a [`Command`] that focuses the [`TextInput`] with the given [`Id`].
-pub fn focus<Message: 'static>(id: Id) -> Command<Message> {
-    Command::widget(operation::focusable::focus(id.0))
+/// Produces a [`Task`] that focuses the [`TextInput`] with the given [`Id`].
+pub fn focus<T>(id: Id) -> Task<T> {
+    Task::effect(Action::widget(operation::focusable::focus(id.0)))
 }
 
-/// Produces a [`Command`] that moves the cursor of the [`TextInput`] with the given [`Id`] to the
+/// Produces a [`Task`] that moves the cursor of the [`TextInput`] with the given [`Id`] to the
 /// end.
-pub fn move_cursor_to_end<Message: 'static>(id: Id) -> Command<Message> {
-    Command::widget(operation::text_input::move_cursor_to_end(id.0))
+pub fn move_cursor_to_end<T>(id: Id) -> Task<T> {
+    Task::effect(Action::widget(operation::text_input::move_cursor_to_end(
+        id.0,
+    )))
 }
 
-/// Produces a [`Command`] that moves the cursor of the [`TextInput`] with the given [`Id`] to the
+/// Produces a [`Task`] that moves the cursor of the [`TextInput`] with the given [`Id`] to the
 /// front.
-pub fn move_cursor_to_front<Message: 'static>(id: Id) -> Command<Message> {
-    Command::widget(operation::text_input::move_cursor_to_front(id.0))
+pub fn move_cursor_to_front<T>(id: Id) -> Task<T> {
+    Task::effect(Action::widget(operation::text_input::move_cursor_to_front(
+        id.0,
+    )))
 }
 
-/// Produces a [`Command`] that moves the cursor of the [`TextInput`] with the given [`Id`] to the
+/// Produces a [`Task`] that moves the cursor of the [`TextInput`] with the given [`Id`] to the
 /// provided position.
-pub fn move_cursor_to<Message: 'static>(
-    id: Id,
-    position: usize,
-) -> Command<Message> {
-    Command::widget(operation::text_input::move_cursor_to(id.0, position))
+pub fn move_cursor_to<T>(id: Id, position: usize) -> Task<T> {
+    Task::effect(Action::widget(operation::text_input::move_cursor_to(
+        id.0, position,
+    )))
 }
 
-/// Produces a [`Command`] that selects all the content of the [`TextInput`] with the given [`Id`].
-pub fn select_all<Message: 'static>(id: Id) -> Command<Message> {
-    Command::widget(operation::text_input::select_all(id.0))
+/// Produces a [`Task`] that selects all the content of the [`TextInput`] with the given [`Id`].
+pub fn select_all<T>(id: Id) -> Task<T> {
+    Task::effect(Action::widget(operation::text_input::select_all(id.0)))
 }
 
 /// The state of a [`TextInput`].

widget/src/themer.rs

@@ -104,7 +104,7 @@ where
         tree: &mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-        operation: &mut dyn Operation<Message>,
+        operation: &mut dyn Operation<()>,
     ) {
         self.content
             .as_widget()
@@ -236,7 +236,7 @@ where
                 &mut self,
                 layout: Layout<'_>,
                 renderer: &Renderer,
-                operation: &mut dyn Operation<Message>,
+                operation: &mut dyn Operation<()>,
             ) {
                 self.content.operate(layout, renderer, operation);
             }

winit/src/application.rs

@@ -19,7 +19,7 @@ use crate::graphics::compositor::{self, Compositor};
 use crate::runtime::clipboard;
 use crate::runtime::program::Program;
 use crate::runtime::user_interface::{self, UserInterface};
-use crate::runtime::{Command, Debug};
+use crate::runtime::{Action, Debug, Task};
 use crate::{Clipboard, Error, Proxy, Settings};
 
 use futures::channel::mpsc;
@@ -36,7 +36,7 @@ use std::sync::Arc;
 /// its own window.
 ///
 /// An [`Application`] can execute asynchronous actions by returning a
-/// [`Command`] in some of its methods.
+/// [`Task`] in some of its methods.
 ///
 /// When using an [`Application`] with the `debug` feature enabled, a debug view
 /// can be toggled by pressing `F12`.
@@ -52,10 +52,10 @@ where
     ///
     /// Here is where you should return the initial state of your app.
     ///
-    /// Additionally, you can return a [`Command`] if you need to perform some
+    /// Additionally, you can return a [`Task`] if you need to perform some
     /// async action in the background on startup. This is useful if you want to
     /// load state from a file, perform an initial HTTP request, etc.
-    fn new(flags: Self::Flags) -> (Self, Command<Self::Message>);
+    fn new(flags: Self::Flags) -> (Self, Task<Self::Message>);
 
     /// Returns the current title of the [`Application`].
     ///
@@ -155,19 +155,23 @@ where
 
     let (proxy, worker) = Proxy::new(event_loop.create_proxy());
 
-    let runtime = {
+    let mut runtime = {
         let executor = E::new().map_err(Error::ExecutorCreationFailed)?;
         executor.spawn(worker);
 
         Runtime::new(executor, proxy.clone())
     };
 
-    let (application, init_command) = {
+    let (application, task) = {
         let flags = settings.flags;
 
         runtime.enter(|| A::new(flags))
     };
 
+    if let Some(stream) = task.into_stream() {
+        runtime.run(stream);
+    }
+
     let id = settings.id;
     let title = application.title();
 
@@ -183,7 +187,6 @@ where
         boot_receiver,
         event_receiver,
         control_sender,
-        init_command,
         settings.fonts,
     ));
 
@@ -193,7 +196,7 @@ where
         instance: std::pin::Pin<Box<F>>,
         context: task::Context<'static>,
         boot: Option<BootConfig<C>>,
-        sender: mpsc::UnboundedSender<winit::event::Event<Message>>,
+        sender: mpsc::UnboundedSender<winit::event::Event<Action<Message>>>,
         receiver: mpsc::UnboundedReceiver<winit::event_loop::ControlFlow>,
         error: Option<Error>,
         #[cfg(target_arch = "wasm32")]
@@ -229,7 +232,7 @@ where
         queued_events: Vec::new(),
     };
 
-    impl<Message, F, C> winit::application::ApplicationHandler<Message>
+    impl<Message, F, C> winit::application::ApplicationHandler<Action<Message>>
         for Runner<Message, F, C>
     where
         F: Future<Output = ()>,
@@ -393,11 +396,11 @@ where
         fn user_event(
             &mut self,
             event_loop: &winit::event_loop::ActiveEventLoop,
-            message: Message,
+            action: Action<Message>,
         ) {
             self.process_event(
                 event_loop,
-                winit::event::Event::UserEvent(message),
+                winit::event::Event::UserEvent(action),
             );
         }
 
@@ -416,7 +419,7 @@ where
         fn process_event(
             &mut self,
             event_loop: &winit::event_loop::ActiveEventLoop,
-            event: winit::event::Event<Message>,
+            event: winit::event::Event<Action<Message>>,
         ) {
             // On Wasm, events may start being processed before the compositor
             // boots up. We simply queue them and process them once ready.
@@ -480,15 +483,14 @@ struct Boot<C> {
 
 async fn run_instance<A, E, C>(
     mut application: A,
-    mut runtime: Runtime<E, Proxy<A::Message>, A::Message>,
+    mut runtime: Runtime<E, Proxy<A::Message>, Action<A::Message>>,
     mut proxy: Proxy<A::Message>,
     mut debug: Debug,
     mut boot: oneshot::Receiver<Boot<C>>,
     mut event_receiver: mpsc::UnboundedReceiver<
-        winit::event::Event<A::Message>,
+        winit::event::Event<Action<A::Message>>,
     >,
     mut control_sender: mpsc::UnboundedSender<winit::event_loop::ControlFlow>,
-    init_command: Command<A::Message>,
     fonts: Vec<Cow<'static, [u8]>>,
 ) where
     A: Application + 'static,
@@ -518,7 +520,7 @@ async fn run_instance<A, E, C>(
     let physical_size = state.physical_size();
 
     let mut clipboard = Clipboard::connect(&window);
-    let mut cache = user_interface::Cache::default();
+    let cache = user_interface::Cache::default();
     let mut surface = compositor.create_surface(
         window.clone(),
         physical_size.width,
@@ -530,22 +532,12 @@ async fn run_instance<A, E, C>(
         window.set_visible(true);
     }
 
-    run_command(
-        &application,
-        &mut compositor,
-        &mut surface,
-        &mut cache,
-        &state,
-        &mut renderer,
-        init_command,
-        &mut runtime,
-        &mut clipboard,
-        &mut should_exit,
-        &mut proxy,
-        &mut debug,
-        &window,
+    runtime.track(
+        application
+            .subscription()
+            .map(Action::Output)
+            .into_recipes(),
     );
-    runtime.track(application.subscription().into_recipes());
 
     let mut user_interface = ManuallyDrop::new(build_user_interface(
         &application,
@@ -581,8 +573,21 @@ async fn run_instance<A, E, C>(
                     ),
                 ));
             }
-            event::Event::UserEvent(message) => {
-                messages.push(message);
+            event::Event::UserEvent(action) => {
+                run_action(
+                    action,
+                    &mut user_interface,
+                    &mut compositor,
+                    &mut surface,
+                    &state,
+                    &mut renderer,
+                    &mut messages,
+                    &mut clipboard,
+                    &mut should_exit,
+                    &mut debug,
+                    &window,
+                );
+
                 user_events += 1;
             }
             event::Event::WindowEvent {
@@ -756,21 +761,14 @@ async fn run_instance<A, E, C>(
                         user_interface::State::Outdated
                     )
                 {
-                    let mut cache =
+                    let cache =
                         ManuallyDrop::into_inner(user_interface).into_cache();
 
                     // Update application
                     update(
                         &mut application,
-                        &mut compositor,
-                        &mut surface,
-                        &mut cache,
                         &mut state,
-                        &mut renderer,
                         &mut runtime,
-                        &mut clipboard,
-                        &mut should_exit,
-                        &mut proxy,
                         &mut debug,
                         &mut messages,
                         &window,
@@ -855,148 +853,114 @@ where
 }
 
 /// Updates an [`Application`] by feeding it the provided messages, spawning any
-/// resulting [`Command`], and tracking its [`Subscription`].
-pub fn update<A: Application, C, E: Executor>(
+/// resulting [`Task`], and tracking its [`Subscription`].
+pub fn update<A: Application, E: Executor>(
     application: &mut A,
-    compositor: &mut C,
-    surface: &mut C::Surface,
-    cache: &mut user_interface::Cache,
     state: &mut State<A>,
-    renderer: &mut A::Renderer,
-    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
-    clipboard: &mut Clipboard,
-    should_exit: &mut bool,
-    proxy: &mut Proxy<A::Message>,
+    runtime: &mut Runtime<E, Proxy<A::Message>, Action<A::Message>>,
     debug: &mut Debug,
     messages: &mut Vec<A::Message>,
     window: &winit::window::Window,
 ) where
-    C: Compositor<Renderer = A::Renderer> + 'static,
     A::Theme: DefaultStyle,
 {
     for message in messages.drain(..) {
         debug.log_message(&message);
 
         debug.update_started();
-        let command = runtime.enter(|| application.update(message));
+        let task = runtime.enter(|| application.update(message));
         debug.update_finished();
 
-        run_command(
-            application,
-            compositor,
-            surface,
-            cache,
-            state,
-            renderer,
-            command,
-            runtime,
-            clipboard,
-            should_exit,
-            proxy,
-            debug,
-            window,
-        );
+        if let Some(stream) = task.into_stream() {
+            runtime.run(stream);
+        }
     }
 
     state.synchronize(application, window);
 
     let subscription = application.subscription();
-    runtime.track(subscription.into_recipes());
+    runtime.track(subscription.map(Action::Output).into_recipes());
 }
 
-/// Runs the actions of a [`Command`].
-pub fn run_command<A, C, E>(
-    application: &A,
+/// Runs the actions of a [`Task`].
+pub fn run_action<A, C>(
+    action: Action<A::Message>,
+    user_interface: &mut UserInterface<'_, A::Message, A::Theme, C::Renderer>,
     compositor: &mut C,
     surface: &mut C::Surface,
-    cache: &mut user_interface::Cache,
     state: &State<A>,
     renderer: &mut A::Renderer,
-    command: Command<A::Message>,
-    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
+    messages: &mut Vec<A::Message>,
     clipboard: &mut Clipboard,
     should_exit: &mut bool,
-    proxy: &mut Proxy<A::Message>,
     debug: &mut Debug,
     window: &winit::window::Window,
 ) where
     A: Application,
-    E: Executor,
     C: Compositor<Renderer = A::Renderer> + 'static,
     A::Theme: DefaultStyle,
 {
-    use crate::runtime::command;
     use crate::runtime::system;
     use crate::runtime::window;
 
-    for action in command.actions() {
     match action {
-            command::Action::Future(future) => {
-                runtime.spawn(future);
+        Action::Clipboard(action) => match action {
+            clipboard::Action::Read { target, channel } => {
+                let _ = channel.send(clipboard.read(target));
             }
-            command::Action::Stream(stream) => {
-                runtime.run(stream);
-            }
-            command::Action::Clipboard(action) => match action {
-                clipboard::Action::Read(tag, kind) => {
-                    let message = tag(clipboard.read(kind));
-
-                    proxy.send(message);
-                }
-                clipboard::Action::Write(contents, kind) => {
-                    clipboard.write(kind, contents);
+            clipboard::Action::Write { target, contents } => {
+                clipboard.write(target, contents);
             }
         },
-            command::Action::Window(action) => match action {
+        Action::Window(action) => match action {
             window::Action::Close(_id) => {
                 *should_exit = true;
             }
             window::Action::Drag(_id) => {
                 let _res = window.drag_window();
             }
-                window::Action::Spawn { .. } => {
+            window::Action::Open { .. } => {
                 log::warn!(
                     "Spawning a window is only available with \
                         multi-window applications."
                 );
             }
             window::Action::Resize(_id, size) => {
-                    let _ =
-                        window.request_inner_size(winit::dpi::LogicalSize {
+                let _ = window.request_inner_size(winit::dpi::LogicalSize {
                     width: size.width,
                     height: size.height,
                 });
             }
-                window::Action::FetchSize(_id, callback) => {
+            window::Action::FetchSize(_id, channel) => {
                 let size =
                     window.inner_size().to_logical(window.scale_factor());
 
-                    proxy.send(callback(Size::new(size.width, size.height)));
+                let _ = channel.send(Size::new(size.width, size.height));
             }
-                window::Action::FetchMaximized(_id, callback) => {
-                    proxy.send(callback(window.is_maximized()));
+            window::Action::FetchMaximized(_id, channel) => {
+                let _ = channel.send(window.is_maximized());
             }
             window::Action::Maximize(_id, maximized) => {
                 window.set_maximized(maximized);
             }
-                window::Action::FetchMinimized(_id, callback) => {
-                    proxy.send(callback(window.is_minimized()));
+            window::Action::FetchMinimized(_id, channel) => {
+                let _ = channel.send(window.is_minimized());
             }
             window::Action::Minimize(_id, minimized) => {
                 window.set_minimized(minimized);
             }
-                window::Action::FetchPosition(_id, callback) => {
+            window::Action::FetchPosition(_id, channel) => {
                 let position = window
                     .inner_position()
                     .map(|position| {
-                            let position = position
-                                .to_logical::<f32>(window.scale_factor());
+                        let position =
+                            position.to_logical::<f32>(window.scale_factor());
 
                         Point::new(position.x, position.y)
                     })
                     .ok();
 
-                    proxy.send(callback(position));
+                let _ = channel.send(position);
             }
             window::Action::Move(_id, position) => {
                 window.set_outer_position(winit::dpi::LogicalPosition {
@@ -1014,14 +978,14 @@ pub fn run_command<A, C, E>(
             window::Action::ChangeIcon(_id, icon) => {
                 window.set_window_icon(conversion::icon(icon));
             }
-                window::Action::FetchMode(_id, tag) => {
+            window::Action::FetchMode(_id, channel) => {
                 let mode = if window.is_visible().unwrap_or(true) {
                     conversion::mode(window.fullscreen())
                 } else {
                     core::window::Mode::Hidden
                 };
 
-                    proxy.send(tag(mode));
+                let _ = channel.send(mode);
             }
             window::Action::ToggleMaximize(_id) => {
                 window.set_maximized(!window.is_maximized());
@@ -1048,18 +1012,18 @@ pub fn run_command<A, C, E>(
                     });
                 }
             }
-                window::Action::FetchId(_id, tag) => {
-                    proxy.send(tag(window.id().into()));
+            window::Action::FetchRawId(_id, channel) => {
+                let _ = channel.send(window.id().into());
             }
-                window::Action::RunWithHandle(_id, tag) => {
+            window::Action::RunWithHandle(_id, f) => {
                 use window::raw_window_handle::HasWindowHandle;
 
                 if let Ok(handle) = window.window_handle() {
-                        proxy.send(tag(handle));
+                    f(handle);
                 }
             }
 
-                window::Action::Screenshot(_id, tag) => {
+            window::Action::Screenshot(_id, channel) => {
                 let bytes = compositor.screenshot(
                     renderer,
                     surface,
@@ -1068,69 +1032,51 @@ pub fn run_command<A, C, E>(
                     &debug.overlay(),
                 );
 
-                    proxy.send(tag(window::Screenshot::new(
+                let _ = channel.send(window::Screenshot::new(
                     bytes,
                     state.physical_size(),
                     state.viewport().scale_factor(),
-                    )));
+                ));
             }
         },
-            command::Action::System(action) => match action {
-                system::Action::QueryInformation(_tag) => {
+        Action::System(action) => match action {
+            system::Action::QueryInformation(_channel) => {
                 #[cfg(feature = "system")]
                 {
                     let graphics_info = compositor.fetch_information();
-                        let mut proxy = proxy.clone();
 
                     let _ = std::thread::spawn(move || {
                         let information =
                             crate::system::information(graphics_info);
 
-                            let message = _tag(information);
-
-                            proxy.send(message);
+                        let _ = _channel.send(information);
                     });
                 }
             }
         },
-            command::Action::Widget(action) => {
-                let mut current_cache = std::mem::take(cache);
-                let mut current_operation = Some(action);
-
-                let mut user_interface = build_user_interface(
-                    application,
-                    current_cache,
-                    renderer,
-                    state.logical_size(),
-                    debug,
-                );
+        Action::Widget(operation) => {
+            let mut current_operation = Some(operation);
 
             while let Some(mut operation) = current_operation.take() {
                 user_interface.operate(renderer, operation.as_mut());
 
                 match operation.finish() {
                     operation::Outcome::None => {}
-                        operation::Outcome::Some(message) => {
-                            proxy.send(message);
-                        }
+                    operation::Outcome::Some(()) => {}
                     operation::Outcome::Chain(next) => {
                         current_operation = Some(next);
                     }
                 }
             }
-
-                current_cache = user_interface.into_cache();
-                *cache = current_cache;
         }
-            command::Action::LoadFont { bytes, tagger } => {
+        Action::LoadFont { bytes, channel } => {
             // TODO: Error handling (?)
             compositor.load_font(bytes);
 
-                proxy.send(tagger(Ok(())));
-            }
-            command::Action::Custom(_) => {
-                log::warn!("Unsupported custom action in `iced_winit` shell");
+            let _ = channel.send(Ok(()));
         }
+        Action::Output(message) => {
+            messages.push(message);
         }
     }
 }

winit/src/multi_window.rs

@@ -21,10 +21,10 @@ use crate::futures::{Executor, Runtime};
 use crate::graphics;
 use crate::graphics::{compositor, Compositor};
 use crate::multi_window::window_manager::WindowManager;
-use crate::runtime::command::{self, Command};
 use crate::runtime::multi_window::Program;
 use crate::runtime::user_interface::{self, UserInterface};
 use crate::runtime::Debug;
+use crate::runtime::{Action, Task};
 use crate::{Clipboard, Error, Proxy, Settings};
 
 pub use crate::application::{default, Appearance, DefaultStyle};
@@ -41,7 +41,7 @@ use std::time::Instant;
 /// its own window.
 ///
 /// An [`Application`] can execute asynchronous actions by returning a
-/// [`Command`] in some of its methods.
+/// [`Task`] in some of its methods.
 ///
 /// When using an [`Application`] with the `debug` feature enabled, a debug view
 /// can be toggled by pressing `F12`.
@@ -57,10 +57,10 @@ where
     ///
     /// Here is where you should return the initial state of your app.
     ///
-    /// Additionally, you can return a [`Command`] if you need to perform some
+    /// Additionally, you can return a [`Task`] if you need to perform some
     /// async action in the background on startup. This is useful if you want to
     /// load state from a file, perform an initial HTTP request, etc.
-    fn new(flags: Self::Flags) -> (Self, Command<Self::Message>);
+    fn new(flags: Self::Flags) -> (Self, Task<Self::Message>);
 
     /// Returns the current title of the [`Application`].
     ///
@@ -127,19 +127,23 @@ where
 
     let (proxy, worker) = Proxy::new(event_loop.create_proxy());
 
-    let runtime = {
+    let mut runtime = {
         let executor = E::new().map_err(Error::ExecutorCreationFailed)?;
         executor.spawn(worker);
 
         Runtime::new(executor, proxy.clone())
     };
 
-    let (application, init_command) = {
+    let (application, task) = {
         let flags = settings.flags;
 
         runtime.enter(|| A::new(flags))
     };
 
+    if let Some(stream) = task.into_stream() {
+        runtime.run(stream);
+    }
+
     let id = settings.id;
     let title = application.title(window::Id::MAIN);
 
@@ -155,7 +159,6 @@ where
         boot_receiver,
         event_receiver,
         control_sender,
-        init_command,
     ));
 
     let context = task::Context::from_waker(task::noop_waker_ref());
@@ -448,13 +451,12 @@ enum Control {
 
 async fn run_instance<A, E, C>(
     mut application: A,
-    mut runtime: Runtime<E, Proxy<A::Message>, A::Message>,
+    mut runtime: Runtime<E, Proxy<A::Message>, Action<A::Message>>,
     mut proxy: Proxy<A::Message>,
     mut debug: Debug,
     mut boot: oneshot::Receiver<Boot<C>>,
-    mut event_receiver: mpsc::UnboundedReceiver<Event<A::Message>>,
+    mut event_receiver: mpsc::UnboundedReceiver<Event<Action<A::Message>>>,
     mut control_sender: mpsc::UnboundedSender<Control>,
-    init_command: Command<A::Message>,
 ) where
     A: Application + 'static,
     E: Executor + 'static,
@@ -511,21 +513,13 @@ async fn run_instance<A, E, C>(
         )]),
     ));
 
-    run_command(
-        &application,
-        &mut compositor,
-        init_command,
-        &mut runtime,
-        &mut clipboard,
-        &mut control_sender,
-        &mut proxy,
-        &mut debug,
-        &mut window_manager,
-        &mut ui_caches,
+    runtime.track(
+        application
+            .subscription()
+            .map(Action::Output)
+            .into_recipes(),
     );
 
-    runtime.track(application.subscription().into_recipes());
-
     let mut messages = Vec::new();
     let mut user_events = 0;
 
@@ -594,8 +588,19 @@ async fn run_instance<A, E, C>(
                             ),
                         );
                     }
-                    event::Event::UserEvent(message) => {
-                        messages.push(message);
+                    event::Event::UserEvent(action) => {
+                        run_action(
+                            action,
+                            &application,
+                            &mut compositor,
+                            &mut messages,
+                            &mut clipboard,
+                            &mut control_sender,
+                            &mut debug,
+                            &mut user_interfaces,
+                            &mut window_manager,
+                            &mut ui_caches,
+                        );
                         user_events += 1;
                     }
                     event::Event::WindowEvent {
@@ -888,7 +893,7 @@ async fn run_instance<A, E, C>(
 
                         // TODO mw application update returns which window IDs to update
                         if !messages.is_empty() || uis_stale {
-                            let mut cached_interfaces: FxHashMap<
+                            let cached_interfaces: FxHashMap<
                                 window::Id,
                                 user_interface::Cache,
                             > = ManuallyDrop::into_inner(user_interfaces)
@@ -899,15 +904,9 @@ async fn run_instance<A, E, C>(
                             // Update application
                             update(
                                 &mut application,
-                                &mut compositor,
                                 &mut runtime,
-                                &mut clipboard,
-                                &mut control_sender,
-                                &mut proxy,
                                 &mut debug,
                                 &mut messages,
-                                &mut window_manager,
-                                &mut cached_interfaces,
                             );
 
                             // we must synchronize all window states with application state after an
@@ -971,63 +970,46 @@ where
     user_interface
 }
 
-/// Updates a multi-window [`Application`] by feeding it messages, spawning any
-/// resulting [`Command`], and tracking its [`Subscription`].
-fn update<A: Application, C, E: Executor>(
+fn update<A: Application, E: Executor>(
     application: &mut A,
-    compositor: &mut C,
-    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
-    clipboard: &mut Clipboard,
-    control_sender: &mut mpsc::UnboundedSender<Control>,
-    proxy: &mut Proxy<A::Message>,
+    runtime: &mut Runtime<E, Proxy<A::Message>, Action<A::Message>>,
     debug: &mut Debug,
     messages: &mut Vec<A::Message>,
-    window_manager: &mut WindowManager<A, C>,
-    ui_caches: &mut FxHashMap<window::Id, user_interface::Cache>,
 ) where
-    C: Compositor<Renderer = A::Renderer> + 'static,
     A::Theme: DefaultStyle,
 {
     for message in messages.drain(..) {
         debug.log_message(&message);
         debug.update_started();
 
-        let command = runtime.enter(|| application.update(message));
+        let task = runtime.enter(|| application.update(message));
         debug.update_finished();
 
-        run_command(
-            application,
-            compositor,
-            command,
-            runtime,
-            clipboard,
-            control_sender,
-            proxy,
-            debug,
-            window_manager,
-            ui_caches,
-        );
+        if let Some(stream) = task.into_stream() {
+            runtime.run(stream);
+        }
     }
 
     let subscription = application.subscription();
-    runtime.track(subscription.into_recipes());
+    runtime.track(subscription.map(Action::Output).into_recipes());
 }
 
-/// Runs the actions of a [`Command`].
-fn run_command<A, C, E>(
+fn run_action<A, C>(
+    action: Action<A::Message>,
     application: &A,
     compositor: &mut C,
-    command: Command<A::Message>,
-    runtime: &mut Runtime<E, Proxy<A::Message>, A::Message>,
+    messages: &mut Vec<A::Message>,
     clipboard: &mut Clipboard,
     control_sender: &mut mpsc::UnboundedSender<Control>,
-    proxy: &mut Proxy<A::Message>,
     debug: &mut Debug,
+    interfaces: &mut FxHashMap<
+        window::Id,
+        UserInterface<'_, A::Message, A::Theme, A::Renderer>,
+    >,
     window_manager: &mut WindowManager<A, C>,
     ui_caches: &mut FxHashMap<window::Id, user_interface::Cache>,
 ) where
     A: Application,
-    E: Executor,
     C: Compositor<Renderer = A::Renderer> + 'static,
     A::Theme: DefaultStyle,
 {
@@ -1035,26 +1017,20 @@ fn run_command<A, C, E>(
     use crate::runtime::system;
     use crate::runtime::window;
 
-    for action in command.actions() {
     match action {
-            command::Action::Future(future) => {
-                runtime.spawn(Box::pin(future));
+        Action::Output(message) => {
+            messages.push(message);
         }
-            command::Action::Stream(stream) => {
-                runtime.run(Box::pin(stream));
+        Action::Clipboard(action) => match action {
+            clipboard::Action::Read { target, channel } => {
+                let _ = channel.send(clipboard.read(target));
             }
-            command::Action::Clipboard(action) => match action {
-                clipboard::Action::Read(tag, kind) => {
-                    let message = tag(clipboard.read(kind));
-
-                    proxy.send(message);
-                }
-                clipboard::Action::Write(contents, kind) => {
-                    clipboard.write(kind, contents);
+            clipboard::Action::Write { target, contents } => {
+                clipboard.write(target, contents);
             }
         },
-            command::Action::Window(action) => match action {
-                window::Action::Spawn(id, settings) => {
+        Action::Window(action) => match action {
+            window::Action::Open(id, settings) => {
                 let monitor = window_manager.last_monitor();
 
                 control_sender
@@ -1091,20 +1067,19 @@ fn run_command<A, C, E>(
                     );
                 }
             }
-                window::Action::FetchSize(id, callback) => {
+            window::Action::FetchSize(id, channel) => {
                 if let Some(window) = window_manager.get_mut(id) {
                     let size = window
                         .raw
                         .inner_size()
                         .to_logical(window.raw.scale_factor());
 
-                        proxy
-                            .send(callback(Size::new(size.width, size.height)));
+                    let _ = channel.send(Size::new(size.width, size.height));
                 }
             }
-                window::Action::FetchMaximized(id, callback) => {
+            window::Action::FetchMaximized(id, channel) => {
                 if let Some(window) = window_manager.get_mut(id) {
-                        proxy.send(callback(window.raw.is_maximized()));
+                    let _ = channel.send(window.raw.is_maximized());
                 }
             }
             window::Action::Maximize(id, maximized) => {
@@ -1112,9 +1087,9 @@ fn run_command<A, C, E>(
                     window.raw.set_maximized(maximized);
                 }
             }
-                window::Action::FetchMinimized(id, callback) => {
+            window::Action::FetchMinimized(id, channel) => {
                 if let Some(window) = window_manager.get_mut(id) {
-                        proxy.send(callback(window.raw.is_minimized()));
+                    let _ = channel.send(window.raw.is_minimized());
                 }
             }
             window::Action::Minimize(id, minimized) => {
@@ -1122,21 +1097,20 @@ fn run_command<A, C, E>(
                     window.raw.set_minimized(minimized);
                 }
             }
-                window::Action::FetchPosition(id, callback) => {
+            window::Action::FetchPosition(id, channel) => {
                 if let Some(window) = window_manager.get_mut(id) {
                     let position = window
                         .raw
                         .inner_position()
                         .map(|position| {
-                                let position = position.to_logical::<f32>(
-                                    window.raw.scale_factor(),
-                                );
+                            let position = position
+                                .to_logical::<f32>(window.raw.scale_factor());
 
                             Point::new(position.x, position.y)
                         })
                         .ok();
 
-                        proxy.send(callback(position));
+                    let _ = channel.send(position);
                 }
             }
             window::Action::Move(id, position) => {
@@ -1163,7 +1137,7 @@ fn run_command<A, C, E>(
                     window.raw.set_window_icon(conversion::icon(icon));
                 }
             }
-                window::Action::FetchMode(id, tag) => {
+            window::Action::FetchMode(id, channel) => {
                 if let Some(window) = window_manager.get_mut(id) {
                     let mode = if window.raw.is_visible().unwrap_or(true) {
                         conversion::mode(window.raw.fullscreen())
@@ -1171,7 +1145,7 @@ fn run_command<A, C, E>(
                         core::window::Mode::Hidden
                     };
 
-                        proxy.send(tag(mode));
+                    let _ = channel.send(mode);
                 }
             }
             window::Action::ToggleMaximize(id) => {
@@ -1217,22 +1191,22 @@ fn run_command<A, C, E>(
                     }
                 }
             }
-                window::Action::FetchId(id, tag) => {
+            window::Action::FetchRawId(id, channel) => {
                 if let Some(window) = window_manager.get_mut(id) {
-                        proxy.send(tag(window.raw.id().into()));
+                    let _ = channel.send(window.raw.id().into());
                 }
             }
-                window::Action::RunWithHandle(id, tag) => {
+            window::Action::RunWithHandle(id, f) => {
                 use window::raw_window_handle::HasWindowHandle;
 
                 if let Some(handle) = window_manager
                     .get_mut(id)
                     .and_then(|window| window.raw.window_handle().ok())
                 {
-                        proxy.send(tag(handle));
+                    f(handle);
                 }
             }
-                window::Action::Screenshot(id, tag) => {
+            window::Action::Screenshot(id, channel) => {
                 if let Some(window) = window_manager.get_mut(id) {
                     let bytes = compositor.screenshot(
                         &mut window.renderer,
@@ -1242,44 +1216,34 @@ fn run_command<A, C, E>(
                         &debug.overlay(),
                     );
 
-                        proxy.send(tag(window::Screenshot::new(
+                    let _ = channel.send(window::Screenshot::new(
                         bytes,
                         window.state.physical_size(),
                         window.state.viewport().scale_factor(),
-                        )));
+                    ));
                 }
             }
         },
-            command::Action::System(action) => match action {
-                system::Action::QueryInformation(_tag) => {
+        Action::System(action) => match action {
+            system::Action::QueryInformation(_channel) => {
                 #[cfg(feature = "system")]
                 {
                     let graphics_info = compositor.fetch_information();
-                        let mut proxy = proxy.clone();
 
                     let _ = std::thread::spawn(move || {
                         let information =
                             crate::system::information(graphics_info);
 
-                            let message = _tag(information);
-
-                            proxy.send(message);
+                        let _ = _channel.send(information);
                     });
                 }
             }
         },
-            command::Action::Widget(action) => {
-                let mut current_operation = Some(action);
-
-                let mut uis = build_user_interfaces(
-                    application,
-                    debug,
-                    window_manager,
-                    std::mem::take(ui_caches),
-                );
+        Action::Widget(operation) => {
+            let mut current_operation = Some(operation);
 
             while let Some(mut operation) = current_operation.take() {
-                    for (id, ui) in uis.iter_mut() {
+                for (id, ui) in interfaces.iter_mut() {
                     if let Some(window) = window_manager.get_mut(*id) {
                         ui.operate(&window.renderer, operation.as_mut());
                     }
@@ -1287,27 +1251,18 @@ fn run_command<A, C, E>(
 
                 match operation.finish() {
                     operation::Outcome::None => {}
-                        operation::Outcome::Some(message) => {
-                            proxy.send(message);
-                        }
+                    operation::Outcome::Some(()) => {}
                     operation::Outcome::Chain(next) => {
                         current_operation = Some(next);
                     }
                 }
             }
-
-                *ui_caches =
-                    uis.drain().map(|(id, ui)| (id, ui.into_cache())).collect();
         }
-            command::Action::LoadFont { bytes, tagger } => {
+        Action::LoadFont { bytes, channel } => {
             // TODO: Error handling (?)
             compositor.load_font(bytes.clone());
 
-                proxy.send(tagger(Ok(())));
-            }
-            command::Action::Custom(_) => {
-                log::warn!("Unsupported custom action in `iced_winit` shell");
-            }
+            let _ = channel.send(Ok(()));
         }
     }
 }

winit/src/proxy.rs

@@ -4,17 +4,18 @@ use crate::futures::futures::{
     task::{Context, Poll},
     Future, Sink, StreamExt,
 };
+use crate::runtime::Action;
 use std::pin::Pin;
 
 /// An event loop proxy with backpressure that implements `Sink`.
 #[derive(Debug)]
-pub struct Proxy<Message: 'static> {
-    raw: winit::event_loop::EventLoopProxy<Message>,
-    sender: mpsc::Sender<Message>,
+pub struct Proxy<T: 'static> {
+    raw: winit::event_loop::EventLoopProxy<Action<T>>,
+    sender: mpsc::Sender<Action<T>>,
     notifier: mpsc::Sender<usize>,
 }
 
-impl<Message: 'static> Clone for Proxy<Message> {
+impl<T: 'static> Clone for Proxy<T> {
     fn clone(&self) -> Self {
         Self {
             raw: self.raw.clone(),
@@ -24,12 +25,12 @@ impl<Message: 'static> Clone for Proxy<Message> {
     }
 }
 
-impl<Message: 'static> Proxy<Message> {
+impl<T: 'static> Proxy<T> {
     const MAX_SIZE: usize = 100;
 
     /// Creates a new [`Proxy`] from an `EventLoopProxy`.
     pub fn new(
-        raw: winit::event_loop::EventLoopProxy<Message>,
+        raw: winit::event_loop::EventLoopProxy<Action<T>>,
     ) -> (Self, impl Future<Output = ()>) {
         let (notifier, mut processed) = mpsc::channel(Self::MAX_SIZE);
         let (sender, mut receiver) = mpsc::channel(Self::MAX_SIZE);
@@ -72,16 +73,16 @@ impl<Message: 'static> Proxy<Message> {
         )
     }
 
-    /// Sends a `Message` to the event loop.
+    /// Sends a value to the event loop.
     ///
     /// Note: This skips the backpressure mechanism with an unbounded
     /// channel. Use sparingly!
-    pub fn send(&mut self, message: Message)
+    pub fn send(&mut self, value: T)
     where
-        Message: std::fmt::Debug,
+        T: std::fmt::Debug,
     {
         self.raw
-            .send_event(message)
+            .send_event(Action::Output(value))
             .expect("Send message to event loop");
     }
 
@@ -92,7 +93,7 @@ impl<Message: 'static> Proxy<Message> {
     }
 }
 
-impl<Message: 'static> Sink<Message> for Proxy<Message> {
+impl<T: 'static> Sink<Action<T>> for Proxy<T> {
     type Error = mpsc::SendError;
 
     fn poll_ready(
@@ -104,9 +105,9 @@ impl<Message: 'static> Sink<Message> for Proxy<Message> {
 
     fn start_send(
         mut self: Pin<&mut Self>,
-        message: Message,
+        action: Action<T>,
     ) -> Result<(), Self::Error> {
-        self.sender.start_send(message)
+        self.sender.start_send(action)
     }
 
     fn poll_flush(

winit/src/system.rs

@@ -1,15 +1,13 @@
 //! Access the native system.
 use crate::graphics::compositor;
-use crate::runtime::command::{self, Command};
 use crate::runtime::system::{Action, Information};
+use crate::runtime::{self, Task};
 
 /// Query for available system information.
-pub fn fetch_information<Message>(
-    f: impl Fn(Information) -> Message + Send + 'static,
-) -> Command<Message> {
-    Command::single(command::Action::System(Action::QueryInformation(
-        Box::new(f),
-    )))
+pub fn fetch_information() -> Task<Information> {
+    Task::oneshot(|channel| {
+        runtime::Action::System(Action::QueryInformation(channel))
+    })
 }
 
 pub(crate) fn information(