diff options
Diffstat (limited to 'pure/src/lib.rs')
| -rw-r--r-- | pure/src/lib.rs | 120 |
1 files changed, 119 insertions, 1 deletions
diff --git a/pure/src/lib.rs b/pure/src/lib.rs index f9f0ae2d..6af74771 100644 --- a/pure/src/lib.rs +++ b/pure/src/lib.rs @@ -1,3 +1,92 @@ +//! Stateless, pure widgets for iced. +//! +//! # The Elm Architecture, purity, and continuity +//! As you may know, applications made with `iced` use [The Elm Architecture]. +//! +//! In a nutshell, this architecture defines the initial state of the application, a way to `view` it, and a way to `update` it after a user interaction. The `update` logic is called after a meaningful user interaction, which in turn updates the state of the application. Then, the `view` logic is executed to redisplay the application. +//! +//! Since `view` logic is only run after an `update`, all of the mutations to the application state must only happen in the `update` logic. If the application state changes anywhere else, the `view` logic will not be rerun and, therefore, the previously generated `view` may stay outdated. +//! +//! However, the `Application` trait in `iced` defines `view` as: +//! +//! ```ignore +//! pub trait Application { +//! fn view(&mut self) -> Element<Self::Message>; +//! } +//! ``` +//! +//! As a consequence, the application state can be mutated in `view` logic. The `view` logic in `iced` is __impure__. +//! +//! This impurity is necessary because `iced` puts the burden of widget __continuity__ on its users. In other words, it's up to you to provide `iced` with the internal state of each widget every time `view` is called. +//! +//! If we take a look at the classic `counter` example: +//! +//! ```ignore +//! struct Counter { +//! value: i32, +//! increment_button: button::State, +//! decrement_button: button::State, +//! } +//! +//! // ... +//! +//! impl Counter { +//! pub fn view(&mut self) -> Column<Message> { +//! Column::new() +//! .push( +//! Button::new(&mut self.increment_button, Text::new("+")) +//! .on_press(Message::IncrementPressed), +//! ) +//! .push(Text::new(self.value.to_string()).size(50)) +//! .push( +//! Button::new(&mut self.decrement_button, Text::new("-")) +//! .on_press(Message::DecrementPressed), +//! ) +//! } +//! } +//! ``` +//! +//! We can see how we need to keep track of the `button::State` of each `Button` in our `Counter` state and provide a mutable reference to the widgets in our `view` logic. The widgets produced by `view` are __stateful__. +//! +//! While this approach forces users to keep track of widget state and causes impurity, I originally chose it because it allows `iced` to directly consume the widget tree produced by `view`. Since there is no internal state decoupled from `view` maintained by the runtime, `iced` does not need to compare (e.g. reconciliate) widget trees in order to ensure continuity. +//! +//! # Stateless widgets +//! As the library matures, the need for some kind of persistent widget data (see #553) between `view` calls becomes more apparent (e.g. incremental rendering, animations, accessibility, etc.). +//! +//! If we are going to end up having persistent widget data anyways... There is no reason to have impure, stateful widgets anymore! +//! +//! And so I started exploring and ended up creating a new subcrate called `iced_pure`, which introduces a completely stateless implementation for every widget in `iced`. +//! +//! With the help of this crate, we can now write a pure `counter` example: +//! +//! ```ignore +//! struct Counter { +//! value: i32, +//! } +//! +//! // ... +//! +//! impl Counter { +//! fn view(&self) -> Column<Message> { +//! Column::new() +//! .push(Button::new("Increment").on_press(Message::IncrementPressed)) +//! .push(Text::new(self.value.to_string()).size(50)) +//! .push(Button::new("Decrement").on_press(Message::DecrementPressed)) +//! } +//! } +//! ``` +//! +//! Notice how we no longer need to keep track of the `button::State`! The widgets in `iced_pure` do not take any mutable application state in `view`. They are __stateless__ widgets. As a consequence, we do not need mutable access to `self` in `view` anymore. `view` becomes __pure__. +//! +//! [The Elm Architecture]: https://guide.elm-lang.org/architecture/ +#![doc( + html_logo_url = "https://raw.githubusercontent.com/iced-rs/iced/9ab6923e943f784985e9ef9ca28b10278297225d/docs/logo.svg" +)] +#![deny(missing_docs)] +#![deny(unused_results)] +#![forbid(unsafe_code)] +#![forbid(rust_2018_idioms)] + pub mod helpers; pub mod overlay; pub mod widget; @@ -16,6 +105,32 @@ use iced_native::mouse; use iced_native::renderer; use iced_native::{Clipboard, Length, Point, Rectangle, Shell}; +/// A bridge between impure and pure widgets. +/// +/// If you already have an existing `iced` application, you do not need to switch completely to the new traits in order to benefit from the `pure` module. Instead, you can leverage the new `Pure` widget to include `pure` widgets in your impure `Application`. +/// +/// For instance, let's say we want to use our pure `Counter` in an impure application: +/// +/// ```ignore +/// use iced_pure::{self, Pure}; +/// +/// struct Impure { +/// state: pure::State, +/// counter: Counter, +/// } +/// +/// impl Sandbox for Impure { +/// // ... +/// +/// pub fn view(&mut self) -> Element<Self::Message> { +/// Pure::new(&mut self.state, self.counter.view()).into() +/// } +/// } +/// ``` +/// +/// [`Pure`] acts as a bridge between pure and impure widgets. It is completely opt-in and can be used to slowly migrate your application to the new architecture. +/// +/// The purification of your application may trigger a bunch of important refactors, since it's far easier to keep your data decoupled from the GUI state with stateless widgets. For this reason, I recommend starting small in the most nested views of your application and slowly expand the purity upwards. pub struct Pure<'a, Message, Renderer> { state: &'a mut State, element: Element<'a, Message, Renderer>, @@ -26,6 +141,7 @@ where Message: 'a, Renderer: iced_native::Renderer + 'a, { + /// Creates a new [`Pure`] widget with the given [`State`] and impure [`Element`]. pub fn new( state: &'a mut State, content: impl Into<Element<'a, Message, Renderer>>, @@ -37,6 +153,7 @@ where } } +/// The internal state of a [`Pure`] widget. pub struct State { state_tree: widget::Tree, } @@ -48,6 +165,7 @@ impl Default for State { } impl State { + /// Creates a new [`State`] for a [`Pure`] widget. pub fn new() -> Self { Self { state_tree: widget::Tree::empty(), @@ -56,7 +174,7 @@ impl State { fn diff<Message, Renderer>( &mut self, - new_element: &Element<Message, Renderer>, + new_element: &Element<'_, Message, Renderer>, ) { self.state_tree.diff(new_element); } |