Replace with function with Function trait

core/src/lib.rs

@@ -94,62 +94,59 @@ pub fn never<T>(never: std::convert::Infallible) -> T {
     match never {}
 }
 
-/// Applies the given prefix value to the provided closure and returns
-/// a new closure that takes the other argument.
+/// A trait extension for binary functions (`Fn(A, B) -> O`).
 ///
-/// This lets you partially "apply" a function—equivalent to currying,
-/// but it only works with binary functions. If you want to apply an
-/// arbitrary number of arguments, use the [`with!`] macro instead.
-///
-/// # When is this useful?
-/// Sometimes you will want to identify the source or target
-/// of some message in your user interface. This can be achieved through
-/// normal means by defining a closure and moving the identifier
-/// inside:
-///
-/// ```rust
-/// # let element: Option<()> = Some(());
-/// # enum Message { ButtonPressed(u32, ()) }
-/// let id = 123;
-///
-/// # let _ = {
-/// element.map(move |result| Message::ButtonPressed(id, result))
-/// # };
-/// ```
-///
-/// That's quite a mouthful. [`with()`] lets you write:
-///
-/// ```rust
-/// # use iced_core::with;
-/// # let element: Option<()> = Some(());
-/// # enum Message { ButtonPressed(u32, ()) }
-/// let id = 123;
-///
-/// # let _ = {
-/// element.map(with(Message::ButtonPressed, id))
-/// # };
-/// ```
-///
-/// Effectively creating the same closure that partially applies
-/// the `id` to the message—but much more concise!
-pub fn with<T, R, O>(
-    mut f: impl FnMut(T, R) -> O,
-    prefix: T,
-) -> impl FnMut(R) -> O
-where
-    T: Copy,
-{
-    move |result| f(prefix, result)
+/// It enables you to use a bunch of nifty functional programming paradigms
+/// that work well with iced.
+pub trait Function<A, B, O> {
+    /// Applies the given first argument to a binary function and returns
+    /// a new function that takes the other argument.
+    ///
+    /// This lets you partially "apply" a function—equivalent to currying,
+    /// but it only works with binary functions. If you want to apply an
+    /// arbitrary number of arguments, create a little struct for them.
+    ///
+    /// # When is this useful?
+    /// Sometimes you will want to identify the source or target
+    /// of some message in your user interface. This can be achieved through
+    /// normal means by defining a closure and moving the identifier
+    /// inside:
+    ///
+    /// ```rust
+    /// # let element: Option<()> = Some(());
+    /// # enum Message { ButtonPressed(u32, ()) }
+    /// let id = 123;
+    ///
+    /// # let _ = {
+    /// element.map(move |result| Message::ButtonPressed(id, result))
+    /// # };
+    /// ```
+    ///
+    /// That's quite a mouthful. [`with`] lets you write:
+    ///
+    /// ```rust
+    /// # use iced_core::Function;
+    /// # let element: Option<()> = Some(());
+    /// # enum Message { ButtonPressed(u32, ()) }
+    /// let id = 123;
+    ///
+    /// # let _ = {
+    /// element.map(Message::ButtonPressed.with(id))
+    /// # };
+    /// ```
+    ///
+    /// Effectively creating the same closure that partially applies
+    /// the `id` to the message—but much more concise!
+    fn with(self, prefix: A) -> impl Fn(B) -> O;
 }
 
-/// Applies the given prefix values to the provided closure in the first
-/// argument and returns a new closure that takes its last argument.
-///
-/// This is a variadic version of [`with()`] which works with any number of
-/// arguments.
-#[macro_export]
-macro_rules! with {
-    ($f:expr, $($x:expr),+ $(,)?) => {
-        move |result| $f($($x),+, result)
-    };
+impl<F, A, B, O> Function<A, B, O> for F
+where
+    F: Fn(A, B) -> O,
+    Self: Sized,
+    A: Copy,
+{
+    fn with(self, prefix: A) -> impl Fn(B) -> O {
+        move |result| self(prefix, result)
+    }
 }

examples/download_progress/src/main.rs

@@ -4,7 +4,7 @@ use download::download;
 
 use iced::task;
 use iced::widget::{button, center, column, progress_bar, text, Column};
-use iced::{with, Center, Element, Right, Task};
+use iced::{Center, Element, Function, Right, Task};
 
 pub fn main() -> iced::Result {
     iced::application(
@@ -52,7 +52,7 @@ impl Example {
 
                 let task = download.start();
 
-                task.map(with(Message::DownloadUpdated, index))
+                task.map(Message::DownloadUpdated.with(index))
             }
             Message::DownloadUpdated(id, update) => {
                 if let Some(download) =

examples/gallery/src/main.rs

@@ -14,7 +14,7 @@ use iced::widget::{
 };
 use iced::window;
 use iced::{
-    color, with, Animation, ContentFit, Element, Fill, Subscription, Task,
+    color, Animation, ContentFit, Element, Fill, Function, Subscription, Task,
     Theme,
 };
 
@@ -100,8 +100,8 @@ impl Gallery {
                         width: Preview::WIDTH,
                         height: Preview::HEIGHT,
                     }),
-                    with(Message::BlurhashDecoded, id),
-                    with(Message::ThumbnailDownloaded, id),
+                    Message::BlurhashDecoded.with(id),
+                    Message::ThumbnailDownloaded.with(id),
                 )
             }
             Message::ImageDownloaded(Ok(rgba)) => {

examples/game_of_life/src/main.rs

@@ -9,7 +9,7 @@ use iced::time::{self, milliseconds};
 use iced::widget::{
     button, checkbox, column, container, pick_list, row, slider, text,
 };
-use iced::{Center, Element, Fill, Subscription, Task, Theme};
+use iced::{Center, Element, Fill, Function, Subscription, Task, Theme};
 
 pub fn main() -> iced::Result {
     tracing_subscriber::fmt::init();
@@ -37,7 +37,7 @@ struct GameOfLife {
 
 #[derive(Debug, Clone)]
 enum Message {
-    Grid(grid::Message, usize),
+    Grid(usize, grid::Message),
     Tick,
     TogglePlayback,
     ToggleGrid(bool),
@@ -61,7 +61,7 @@ impl GameOfLife {
 
     fn update(&mut self, message: Message) -> Task<Message> {
         match message {
-            Message::Grid(message, version) => {
+            Message::Grid(version, message) => {
                 if version == self.version {
                     self.grid.update(message);
                 }
@@ -78,9 +78,7 @@ impl GameOfLife {
 
                     let version = self.version;
 
-                    return Task::perform(task, move |message| {
-                        Message::Grid(message, version)
-                    });
+                    return Task::perform(task, Message::Grid.with(version));
                 }
             }
             Message::TogglePlayback => {
@@ -129,9 +127,7 @@ impl GameOfLife {
         );
 
         let content = column![
-            self.grid
-                .view()
-                .map(move |message| Message::Grid(message, version)),
+            self.grid.view().map(Message::Grid.with(version)),
             controls,
         ]
         .height(Fill);

examples/multi_window/src/main.rs

@@ -3,7 +3,9 @@ use iced::widget::{
     text_input,
 };
 use iced::window;
-use iced::{Center, Element, Fill, Subscription, Task, Theme, Vector};
+use iced::{
+    Center, Element, Fill, Function, Subscription, Task, Theme, Vector,
+};
 
 use std::collections::BTreeMap;
 
@@ -169,7 +171,7 @@ impl Window {
         let scale_input = column![
             text("Window scale factor:"),
             text_input("Window Scale", &self.scale_input)
-                .on_input(move |msg| { Message::ScaleInputChanged(id, msg) })
+                .on_input(Message::ScaleInputChanged.with(id))
                 .on_submit(Message::ScaleChanged(
                     id,
                     self.scale_input.to_string()
@@ -179,7 +181,7 @@ impl Window {
         let title_input = column![
             text("Window title:"),
             text_input("Window Title", &self.title)
-                .on_input(move |msg| { Message::TitleChanged(id, msg) })
+                .on_input(Message::TitleChanged.with(id))
                 .id(format!("input-{id}"))
         ];
 

examples/todos/src/main.rs

@@ -4,7 +4,9 @@ use iced::widget::{
     scrollable, text, text_input, Text,
 };
 use iced::window;
-use iced::{Center, Element, Fill, Font, Subscription, Task as Command};
+use iced::{
+    Center, Element, Fill, Font, Function, Subscription, Task as Command,
+};
 
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
@@ -215,9 +217,8 @@ impl Todos {
                             .map(|(i, task)| {
                                 (
                                     task.id,
-                                    task.view(i).map(move |message| {
-                                        Message::TaskMessage(i, message)
-                                    }),
+                                    task.view(i)
+                                        .map(Message::TaskMessage.with(i)),
                                 )
                             }),
                     )

src/lib.rs

@@ -505,9 +505,9 @@ pub use crate::core::gradient;
 pub use crate::core::padding;
 pub use crate::core::theme;
 pub use crate::core::{
-    never, with, Alignment, Animation, Background, Border, Color, ContentFit,
-    Degrees, Gradient, Length, Padding, Pixels, Point, Radians, Rectangle,
-    Rotation, Settings, Shadow, Size, Theme, Transformation, Vector,
+    never, Alignment, Animation, Background, Border, Color, ContentFit,
+    Degrees, Function, Gradient, Length, Padding, Pixels, Point, Radians,
+    Rectangle, Rotation, Settings, Shadow, Size, Theme, Transformation, Vector,
 };
 pub use crate::runtime::exit;
 pub use iced_futures::Subscription;