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|
//! Listen to external events in your application.
/// A request to listen to external events.
///
/// Besides performing async actions on demand with [`Command`], most
/// applications also need to listen to external events passively.
///
/// A [`Subscription`] is normally provided to some runtime, like a [`Command`],
/// and it will generate events as long as the user keeps requesting it.
///
/// For instance, you can use a [`Subscription`] to listen to a WebSocket
/// connection, keyboard presses, mouse events, time ticks, etc.
///
/// This type is normally aliased by runtimes with a specific `Input` and/or
/// `Hasher`.
///
/// [`Command`]: ../struct.Command.html
/// [`Subscription`]: struct.Subscription.html
pub struct Subscription<Hasher, Input, Output> {
recipes: Vec<Box<dyn Recipe<Hasher, Input, Output = Output>>>,
}
impl<H, I, O> Subscription<H, I, O>
where
H: std::hash::Hasher,
{
/// Returns an empty [`Subscription`] that will not produce any output.
///
/// [`Subscription`]: struct.Subscription.html
pub fn none() -> Self {
Self {
recipes: Vec::new(),
}
}
/// Creates a [`Subscription`] from a [`Recipe`] describing it.
///
/// [`Subscription`]: struct.Subscription.html
/// [`Recipe`]: trait.Recipe.html
pub fn from_recipe(
recipe: impl Recipe<H, I, Output = O> + 'static,
) -> Self {
Self {
recipes: vec![Box::new(recipe)],
}
}
/// Batches all the provided subscriptions and returns the resulting
/// [`Subscription`].
///
/// [`Subscription`]: struct.Subscription.html
pub fn batch(
subscriptions: impl Iterator<Item = Subscription<H, I, O>>,
) -> Self {
Self {
recipes: subscriptions
.flat_map(|subscription| subscription.recipes)
.collect(),
}
}
/// Returns the different recipes of the [`Subscription`].
///
/// [`Subscription`]: struct.Subscription.html
pub fn recipes(self) -> Vec<Box<dyn Recipe<H, I, Output = O>>> {
self.recipes
}
/// Transforms the [`Subscription`] output with the given function.
///
/// [`Subscription`]: struct.Subscription.html
pub fn map<A>(
mut self,
f: impl Fn(O) -> A + Send + Sync + 'static,
) -> Subscription<H, I, A>
where
H: 'static,
I: 'static,
O: 'static,
A: 'static,
{
let function = std::sync::Arc::new(f);
Subscription {
recipes: self
.recipes
.drain(..)
.map(|recipe| {
Box::new(Map::new(recipe, function.clone()))
as Box<dyn Recipe<H, I, Output = A>>
})
.collect(),
}
}
}
impl<I, O, H> std::fmt::Debug for Subscription<I, O, H> {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
f.debug_struct("Subscription").finish()
}
}
/// The description of a [`Subscription`].
///
/// A [`Recipe`] is the internal definition of a [`Subscription`]. It is used
/// by runtimes to run and identify subscriptions. You can use it to create your
/// own!
///
/// [`Subscription`]: struct.Subscription.html
/// [`Recipe`]: trait.Recipe.html
pub trait Recipe<Hasher: std::hash::Hasher, Input> {
/// The events that will be produced by a [`Subscription`] with this
/// [`Recipe`].
///
/// [`Subscription`]: struct.Subscription.html
/// [`Recipe`]: trait.Recipe.html
type Output;
/// Hashes the [`Recipe`].
///
/// This is used by runtimes to uniquely identify a [`Subscription`].
///
/// [`Subscription`]: struct.Subscription.html
/// [`Recipe`]: trait.Recipe.html
fn hash(&self, state: &mut Hasher);
/// Executes the [`Recipe`] and produces the stream of events of its
/// [`Subscription`].
///
/// It receives some generic `Input`, which is normally defined by runtimes.
///
/// [`Subscription`]: struct.Subscription.html
/// [`Recipe`]: trait.Recipe.html
fn stream(
self: Box<Self>,
input: Input,
) -> futures::stream::BoxStream<'static, Self::Output>;
}
struct Map<Hasher, Input, A, B> {
recipe: Box<dyn Recipe<Hasher, Input, Output = A>>,
mapper: std::sync::Arc<dyn Fn(A) -> B + Send + Sync>,
}
impl<H, I, A, B> Map<H, I, A, B> {
fn new(
recipe: Box<dyn Recipe<H, I, Output = A>>,
mapper: std::sync::Arc<dyn Fn(A) -> B + Send + Sync + 'static>,
) -> Self {
Map { recipe, mapper }
}
}
impl<H, I, A, B> Recipe<H, I> for Map<H, I, A, B>
where
A: 'static,
B: 'static,
H: std::hash::Hasher,
{
type Output = B;
fn hash(&self, state: &mut H) {
use std::hash::Hash;
std::any::TypeId::of::<B>().hash(state);
self.recipe.hash(state);
}
fn stream(
self: Box<Self>,
input: I,
) -> futures::stream::BoxStream<'static, Self::Output> {
use futures::StreamExt;
let mapper = self.mapper;
self.recipe
.stream(input)
.map(move |element| mapper(element))
.boxed()
}
}
|
