forked from mirror/async-std
52 lines
1.2 KiB
Rust
52 lines
1.2 KiB
Rust
use core::future::Future;
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use core::pin::Pin;
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use core::task::{Context, Poll};
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use pin_project_lite::pin_project;
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use crate::stream::DoubleEndedStream;
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pin_project! {
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#[doc(hidden)]
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#[allow(missing_debug_implementations)]
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pub struct RFoldFuture<S, F, B> {
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#[pin]
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stream: S,
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f: F,
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acc: Option<B>,
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}
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}
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impl<S, F, B> RFoldFuture<S, F, B> {
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pub(super) fn new(stream: S, init: B, f: F) -> Self {
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RFoldFuture {
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stream,
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f,
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acc: Some(init),
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}
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}
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}
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impl<S, F, B> Future for RFoldFuture<S, F, B>
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where
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S: DoubleEndedStream + Sized,
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F: FnMut(B, S::Item) -> B,
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{
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type Output = B;
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fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
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let mut this = self.project();
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loop {
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let next = futures_core::ready!(this.stream.as_mut().poll_next_back(cx));
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match next {
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Some(v) => {
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let old = this.acc.take().unwrap();
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let new = (this.f)(old, v);
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*this.acc = Some(new);
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}
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None => return Poll::Ready(this.acc.take().unwrap()),
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}
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}
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}
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}
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