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A more general function than `from_fn` (rust-lang#2254), as suggested in rust-lang#2254 (comment)
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,83 @@ | ||
| use core::{future::Future, pin::Pin}; | ||
| use futures_core::task::{Context, Poll}; | ||
| use futures_sink::Sink; | ||
| use pin_project::pin_project; | ||
|
|
||
| /// Sink for the [`unfold`] function. | ||
| #[pin_project] | ||
| #[derive(Debug)] | ||
| #[must_use = "sinks do nothing unless polled"] | ||
| pub struct Unfold<T, F, R> { | ||
| state: Option<T>, | ||
| function: F, | ||
| #[pin] | ||
| future: Option<R>, | ||
| } | ||
|
|
||
| /// Create a sink from a function which processes one item at a time. | ||
| /// | ||
| /// # Examples | ||
| /// | ||
| /// ``` | ||
| /// # futures::executor::block_on(async { | ||
| /// use futures::sink::{self, SinkExt}; | ||
| /// | ||
| /// let unfold = sink::unfold(0, |mut sum, i: i32| { | ||
| /// async move { | ||
| /// sum += i; | ||
| /// eprintln!("{}", i); | ||
| /// Ok::<_, futures::never::Never>(sum) | ||
| /// } | ||
| /// }); | ||
| /// futures::pin_mut!(unfold); | ||
| /// unfold.send(5).await?; | ||
| /// # Ok::<(), futures::never::Never>(()) }).unwrap(); | ||
| /// ``` | ||
| pub fn unfold<T, F, R>(init: T, function: F) -> Unfold<T, F, R> { | ||
| Unfold { | ||
| state: Some(init), | ||
| function, | ||
| future: None, | ||
| } | ||
| } | ||
|
|
||
| impl<T, F, R, Item, E> Sink<Item> for Unfold<T, F, R> | ||
| where | ||
| F: FnMut(T, Item) -> R, | ||
| R: Future<Output = Result<T, E>>, | ||
| { | ||
| type Error = E; | ||
|
|
||
| fn poll_ready(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { | ||
| self.poll_flush(cx) | ||
| } | ||
|
|
||
| fn start_send(self: Pin<&mut Self>, item: Item) -> Result<(), Self::Error> { | ||
| let mut this = self.project(); | ||
| debug_assert!(this.future.is_none()); | ||
| let future = (this.function)(this.state.take().unwrap(), item); | ||
| this.future.set(Some(future)); | ||
| Ok(()) | ||
| } | ||
|
|
||
| fn poll_flush(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { | ||
| let mut this = self.project(); | ||
| Poll::Ready(if let Some(future) = this.future.as_mut().as_pin_mut() { | ||
| let result = match ready!(future.poll(cx)) { | ||
| Ok(state) => { | ||
| *this.state = Some(state); | ||
| Ok(()) | ||
| } | ||
| Err(err) => Err(err), | ||
| }; | ||
| this.future.set(None); | ||
| result | ||
| } else { | ||
| Ok(()) | ||
| }) | ||
| } | ||
|
|
||
| fn poll_close(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> { | ||
| self.poll_flush(cx) | ||
| } | ||
| } |
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