Make Command implementations platform-specific

This allows us to introduce a platform-specific `Action` to both `iced_native`
and `iced_web` and remove the `Clipboard` from `Application::update` to maintain
purity.

Additionally, this should let us implement further actions to let users query
and modify the shell environment (e.g. window, clipboard, and more!)

native/src/clipboard.rs

@@ -21,3 +21,20 @@ impl Clipboard for Null {
 
     fn write(&mut self, _contents: String) {}
 }
+
+pub enum Action<T> {
+    Read(Box<dyn Fn(Option<String>) -> T>),
+    Write(Box<dyn Fn(String) -> T>),
+}
+
+impl<T> Action<T> {
+    pub fn map<A>(self, f: impl Fn(T) -> A + 'static + Send + Sync) -> Action<A>
+    where
+        T: 'static,
+    {
+        match self {
+            Self::Read(o) => Action::Read(Box::new(move |s| f(o(s)))),
+            Self::Write(o) => Action::Write(Box::new(move |s| f(o(s)))),
+        }
+    }
+}

native/src/command.rs

@@ -0,0 +1,77 @@
+mod action;
+
+pub use action::Action;
+
+use std::future::Future;
+
+/// A set of asynchronous actions to be performed by some runtime.
+pub enum Command<T> {
+    None,
+    Single(Action<T>),
+    Batch(Vec<Action<T>>),
+}
+
+impl<T> Command<T> {
+    /// Creates an empty [`Command`].
+    ///
+    /// In other words, a [`Command`] that does nothing.
+    pub fn none() -> Self {
+        Self::None
+    }
+
+    /// Creates a [`Command`] that performs the action of the given future.
+    pub fn perform<A>(
+        future: impl Future<Output = T> + 'static + Send,
+        f: impl Fn(T) -> A + 'static + Send,
+    ) -> Command<A> {
+        use iced_futures::futures::FutureExt;
+
+        Command::Single(Action::Future(Box::pin(future.map(f))))
+    }
+
+    /// Applies a transformation to the result of a [`Command`].
+    pub fn map<A>(
+        self,
+        f: impl Fn(T) -> A + 'static + Send + Sync + Clone,
+    ) -> Command<A>
+    where
+        T: 'static,
+    {
+        match self {
+            Self::None => Command::None,
+            Self::Single(action) => Command::Single(action.map(f)),
+            Self::Batch(batch) => Command::Batch(
+                batch
+                    .into_iter()
+                    .map(|action| action.map(f.clone()))
+                    .collect(),
+            ),
+        }
+    }
+
+    /// 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 in commands {
+            match command {
+                Self::None => {}
+                Self::Single(command) => batch.push(command),
+                Self::Batch(commands) => batch.extend(commands),
+            }
+        }
+
+        Self::Batch(batch)
+    }
+
+    pub fn actions(self) -> Vec<Action<T>> {
+        match self {
+            Self::None => Vec::new(),
+            Self::Single(action) => vec![action],
+            Self::Batch(batch) => batch,
+        }
+    }
+}

native/src/command/action.rs

@@ -0,0 +1,24 @@
+use crate::clipboard;
+use crate::window;
+
+pub enum Action<T> {
+    Future(iced_futures::BoxFuture<T>),
+    Clipboard(clipboard::Action<T>),
+    Window(window::Action),
+}
+
+impl<T> Action<T> {
+    /// Applies a transformation to the result of a [`Command`].
+    pub fn map<A>(self, f: impl Fn(T) -> A + 'static + Send + Sync) -> Action<A>
+    where
+        T: 'static,
+    {
+        use iced_futures::futures::FutureExt;
+
+        match self {
+            Self::Future(future) => Action::Future(Box::pin(future.map(f))),
+            Self::Clipboard(action) => Action::Clipboard(action.map(f)),
+            Self::Window(window) => Action::Window(window),
+        }
+    }
+}

native/src/lib.rs

@@ -28,12 +28,13 @@
 //! [`druid`]: https://github.com/xi-editor/druid
 //! [`raw-window-handle`]: https://github.com/rust-windowing/raw-window-handle
 //! [renderer]: crate::renderer
-#![deny(missing_docs)]
-#![deny(missing_debug_implementations)]
+//#![deny(missing_docs)]
+//#![deny(missing_debug_implementations)]
 #![deny(unused_results)]
 #![forbid(unsafe_code)]
 #![forbid(rust_2018_idioms)]
 pub mod clipboard;
+pub mod command;
 pub mod event;
 pub mod keyboard;
 pub mod layout;
@@ -64,12 +65,13 @@ pub use iced_core::{
     menu, Align, Background, Color, Font, HorizontalAlignment, Length, Menu,
     Padding, Point, Rectangle, Size, Vector, VerticalAlignment,
 };
-pub use iced_futures::{executor, futures, Command};
+pub use iced_futures::{executor, futures};
 
 #[doc(no_inline)]
 pub use executor::Executor;
 
 pub use clipboard::Clipboard;
+pub use command::Command;
 pub use debug::Debug;
 pub use element::Element;
 pub use event::Event;

native/src/program.rs

@@ -1,5 +1,5 @@
 //! Build interactive programs using The Elm Architecture.
-use crate::{Clipboard, Command, Element, Renderer};
+use crate::{Command, Element, Renderer};
 
 mod state;
 
@@ -13,9 +13,6 @@ pub trait Program: Sized {
     /// The type of __messages__ your [`Program`] will produce.
     type Message: std::fmt::Debug + Clone + Send;
 
-    /// The type of [`Clipboard`] your [`Program`] will use.
-    type Clipboard: Clipboard;
-
     /// Handles a __message__ and updates the state of the [`Program`].
     ///
     /// This is where you define your __update logic__. All the __messages__,
@@ -24,11 +21,7 @@ pub trait Program: Sized {
     ///
     /// Any [`Command`] returned will be executed immediately in the
     /// background by shells.
-    fn update(
-        &mut self,
-        message: Self::Message,
-        clipboard: &mut Self::Clipboard,
-    ) -> Command<Self::Message>;
+    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
 
     /// Returns the widgets to display in the [`Program`].
     ///

native/src/program/state.rs

@@ -1,5 +1,6 @@
 use crate::{
-    Cache, Command, Debug, Event, Point, Program, Renderer, Size, UserInterface,
+    Cache, Clipboard, Command, Debug, Event, Point, Program, Renderer, Size,
+    UserInterface,
 };
 
 /// The execution state of a [`Program`]. It leverages caching, event
@@ -91,7 +92,7 @@ where
         bounds: Size,
         cursor_position: Point,
         renderer: &mut P::Renderer,
-        clipboard: &mut P::Clipboard,
+        clipboard: &mut dyn Clipboard,
         debug: &mut Debug,
     ) -> Option<Command<P::Message>> {
         let mut user_interface = build_user_interface(
@@ -135,7 +136,7 @@ where
                     debug.log_message(&message);
 
                     debug.update_started();
-                    let command = self.program.update(message, clipboard);
+                    let command = self.program.update(message);
                     debug.update_finished();
 
                     command

native/src/window.rs

@@ -1,4 +1,6 @@
 //! Build window-based GUI applications.
+mod action;
 mod event;
 
+pub use action::Action;
 pub use event::Event;

native/src/window/action.rs

@@ -0,0 +1,18 @@
+/// An operation to be performed on some window.
+#[derive(Debug)]
+pub enum Action {
+    /// Resize the window.
+    Resize {
+        /// The new logical width of the window
+        width: u32,
+        /// The new logical height of the window
+        height: u32,
+    },
+    /// Move the window.
+    Move {
+        /// The new logical x location of the window
+        x: i32,
+        /// The new logical y location of the window
+        y: i32,
+    },
+}

native/src/window/event.rs

@@ -13,10 +13,9 @@ pub enum Event {
 
     /// A window was resized.
     Resized {
-        /// The new width of the window (in units)
+        /// The new logical width of the window
         width: u32,
-
-        /// The new height of the window (in units)
+        /// The new logical height of the window
         height: u32,
     },