diff options
Diffstat (limited to 'third_party/rust/futures-util/src/stream/poll_fn.rs')
-rw-r--r-- | third_party/rust/futures-util/src/stream/poll_fn.rs | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/third_party/rust/futures-util/src/stream/poll_fn.rs b/third_party/rust/futures-util/src/stream/poll_fn.rs new file mode 100644 index 0000000000..b9bd7d1664 --- /dev/null +++ b/third_party/rust/futures-util/src/stream/poll_fn.rs @@ -0,0 +1,57 @@ +//! Definition of the `PollFn` combinator + +use super::assert_stream; +use core::fmt; +use core::pin::Pin; +use futures_core::stream::Stream; +use futures_core::task::{Context, Poll}; + +/// Stream for the [`poll_fn`] function. +#[must_use = "streams do nothing unless polled"] +pub struct PollFn<F> { + f: F, +} + +impl<F> Unpin for PollFn<F> {} + +impl<F> fmt::Debug for PollFn<F> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("PollFn").finish() + } +} + +/// Creates a new stream wrapping a function returning `Poll<Option<T>>`. +/// +/// Polling the returned stream calls the wrapped function. +/// +/// # Examples +/// +/// ``` +/// use futures::stream::poll_fn; +/// use futures::task::Poll; +/// +/// let mut counter = 1usize; +/// +/// let read_stream = poll_fn(move |_| -> Poll<Option<String>> { +/// if counter == 0 { return Poll::Ready(None); } +/// counter -= 1; +/// Poll::Ready(Some("Hello, World!".to_owned())) +/// }); +/// ``` +pub fn poll_fn<T, F>(f: F) -> PollFn<F> +where + F: FnMut(&mut Context<'_>) -> Poll<Option<T>>, +{ + assert_stream::<T, _>(PollFn { f }) +} + +impl<T, F> Stream for PollFn<F> +where + F: FnMut(&mut Context<'_>) -> Poll<Option<T>>, +{ + type Item = T; + + fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> { + (&mut self.f)(cx) + } +} |