forked from mirror/async-std
Merge #40
40: Add initial Fuse implementation for Stream r=yoshuawuyts a=spacejam @matklad does this address your use case? Co-authored-by: Tyler Neely <tyler.neely@ferrous-systems.com> Co-authored-by: Yoshua Wuyts <yoshuawuyts@gmail.com>
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commit
4f9e7d39e2
3 changed files with 65 additions and 1 deletions
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@ -27,7 +27,7 @@ pub use from_stream::FromStream;
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pub use into_stream::IntoStream;
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pub use once::{once, Once};
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pub use repeat::{repeat, Repeat};
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pub use stream::{Scan, Stream, Take, Zip};
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pub use stream::{Fuse, Scan, Stream, Take, Zip};
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mod double_ended_stream;
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mod empty;
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33
src/stream/stream/fuse.rs
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33
src/stream/stream/fuse.rs
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@ -0,0 +1,33 @@
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use std::pin::Pin;
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use std::task::{Context, Poll};
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/// A `Stream` that is permanently closed once a single call to `poll` results in
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/// `Poll::Ready(None)`, returning `Poll::Ready(None)` for all future calls to `poll`.
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#[derive(Clone, Debug)]
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pub struct Fuse<S> {
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pub(crate) stream: S,
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pub(crate) done: bool,
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}
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impl<S: Unpin> Unpin for Fuse<S> {}
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impl<S: futures_core::Stream> Fuse<S> {
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pin_utils::unsafe_pinned!(stream: S);
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pin_utils::unsafe_unpinned!(done: bool);
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}
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impl<S: futures_core::Stream> futures_core::Stream for Fuse<S> {
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type Item = S::Item;
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fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<S::Item>> {
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if self.done {
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Poll::Ready(None)
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} else {
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let next = futures_core::ready!(self.as_mut().stream().poll_next(cx));
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if next.is_none() {
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*self.as_mut().done() = true;
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}
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Poll::Ready(next)
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}
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}
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}
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@ -28,6 +28,7 @@ mod filter_map;
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mod find;
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mod find_map;
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mod fold;
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mod fuse;
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mod min_by;
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mod next;
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mod nth;
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@ -35,6 +36,7 @@ mod scan;
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mod take;
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mod zip;
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pub use fuse::Fuse;
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pub use scan::Scan;
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pub use take::Take;
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pub use zip::Zip;
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@ -246,6 +248,35 @@ pub trait Stream {
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Enumerate::new(self)
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}
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/// Transforms this `Stream` into a "fused" `Stream` such that after the first time `poll`
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/// returns `Poll::Ready(None)`, all future calls to `poll` will also return
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/// `Poll::Ready(None)`.
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///
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/// # Examples
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///
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/// ```
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/// # fn main() { async_std::task::block_on(async {
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/// #
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/// use async_std::prelude::*;
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/// use async_std::stream;
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///
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/// let mut s = stream::once(1).fuse();
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/// assert_eq!(s.next().await, Some(1));
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/// assert_eq!(s.next().await, None);
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/// assert_eq!(s.next().await, None);
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/// #
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/// # }) }
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/// ```
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fn fuse(self) -> Fuse<Self>
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where
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Self: Sized,
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{
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Fuse {
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stream: self,
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done: false,
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}
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}
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/// Both filters and maps a stream.
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///
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/// # Examples
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