| use crate::Stream; |
| |
| use core::future::Future; |
| use core::marker::PhantomPinned; |
| use core::pin::Pin; |
| use core::task::{Context, Poll}; |
| use pin_project_lite::pin_project; |
| |
| pin_project! { |
| /// Future returned by the [`fold`](super::StreamExt::fold) method. |
| #[derive(Debug)] |
| #[must_use = "futures do nothing unless you `.await` or poll them"] |
| pub struct FoldFuture<St, B, F> { |
| #[pin] |
| stream: St, |
| acc: Option<B>, |
| f: F, |
| // Make this future `!Unpin` for compatibility with async trait methods. |
| #[pin] |
| _pin: PhantomPinned, |
| } |
| } |
| |
| impl<St, B, F> FoldFuture<St, B, F> { |
| pub(super) fn new(stream: St, init: B, f: F) -> Self { |
| Self { |
| stream, |
| acc: Some(init), |
| f, |
| _pin: PhantomPinned, |
| } |
| } |
| } |
| |
| impl<St, B, F> Future for FoldFuture<St, B, F> |
| where |
| St: Stream, |
| F: FnMut(B, St::Item) -> B, |
| { |
| type Output = B; |
| |
| fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> { |
| let mut me = self.project(); |
| loop { |
| let next = ready!(me.stream.as_mut().poll_next(cx)); |
| |
| match next { |
| Some(v) => { |
| let old = me.acc.take().unwrap(); |
| let new = (me.f)(old, v); |
| *me.acc = Some(new); |
| } |
| None => return Poll::Ready(me.acc.take().unwrap()), |
| } |
| } |
| } |
| } |