| use core::pin::Pin; |
| use futures_core::future::{Future, FusedFuture}; |
| use futures_core::task::{Context, Poll}; |
| use pin_project::pin_project; |
| |
| /// Future for the [`fuse`](super::FutureExt::fuse) method. |
| #[pin_project] |
| #[derive(Debug)] |
| #[must_use = "futures do nothing unless you `.await` or poll them"] |
| pub struct Fuse<Fut>(#[pin] Option<Fut>); |
| |
| impl<Fut> Fuse<Fut> { |
| pub(super) fn new(f: Fut) -> Fuse<Fut> { |
| Fuse(Some(f)) |
| } |
| } |
| |
| impl<Fut: Future> Fuse<Fut> { |
| /// Creates a new `Fuse`-wrapped future which is already terminated. |
| /// |
| /// This can be useful in combination with looping and the `select!` |
| /// macro, which bypasses terminated futures. |
| /// |
| /// # Examples |
| /// |
| /// ``` |
| /// # futures::executor::block_on(async { |
| /// use futures::channel::mpsc; |
| /// use futures::future::{Fuse, FusedFuture, FutureExt}; |
| /// use futures::select; |
| /// use futures::stream::StreamExt; |
| /// use futures::pin_mut; |
| /// |
| /// let (sender, mut stream) = mpsc::unbounded(); |
| /// |
| /// // Send a few messages into the stream |
| /// sender.unbounded_send(()).unwrap(); |
| /// sender.unbounded_send(()).unwrap(); |
| /// drop(sender); |
| /// |
| /// // Use `Fuse::terminated()` to create an already-terminated future |
| /// // which may be instantiated later. |
| /// let foo_printer = Fuse::terminated(); |
| /// pin_mut!(foo_printer); |
| /// |
| /// loop { |
| /// select! { |
| /// _ = foo_printer => {}, |
| /// () = stream.select_next_some() => { |
| /// if !foo_printer.is_terminated() { |
| /// println!("Foo is already being printed!"); |
| /// } else { |
| /// foo_printer.set(async { |
| /// // do some other async operations |
| /// println!("Printing foo from `foo_printer` future"); |
| /// }.fuse()); |
| /// } |
| /// }, |
| /// complete => break, // `foo_printer` is terminated and the stream is done |
| /// } |
| /// } |
| /// # }); |
| /// ``` |
| pub fn terminated() -> Fuse<Fut> { |
| Fuse(None) |
| } |
| } |
| |
| impl<Fut: Future> FusedFuture for Fuse<Fut> { |
| fn is_terminated(&self) -> bool { |
| self.0.is_none() |
| } |
| } |
| |
| impl<Fut: Future> Future for Fuse<Fut> { |
| type Output = Fut::Output; |
| |
| fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Fut::Output> { |
| Poll::Ready(match self.as_mut().project().0.as_pin_mut() { |
| Some(fut) => { |
| let output = ready!(fut.poll(cx)); |
| self.project().0.set(None); |
| output |
| }, |
| None => return Poll::Pending, |
| }) |
| } |
| } |