//! # 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changes anywhere else, the `view` logic will not be rerun and, therefore, the previously generated `view` may stay outdated.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:
//! 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:
//! 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/
/// 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:
/// [`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.
