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Diffstat (limited to 'library/core/src/future/poll_fn.rs')
-rw-r--r-- | library/core/src/future/poll_fn.rs | 63 |
1 files changed, 63 insertions, 0 deletions
diff --git a/library/core/src/future/poll_fn.rs b/library/core/src/future/poll_fn.rs new file mode 100644 index 000000000..db2a52332 --- /dev/null +++ b/library/core/src/future/poll_fn.rs @@ -0,0 +1,63 @@ +use crate::fmt; +use crate::future::Future; +use crate::pin::Pin; +use crate::task::{Context, Poll}; + +/// Creates a future that wraps a function returning [`Poll`]. +/// +/// Polling the future delegates to the wrapped function. +/// +/// # Examples +/// +/// ``` +/// # async fn run() { +/// use core::future::poll_fn; +/// use std::task::{Context, Poll}; +/// +/// fn read_line(_cx: &mut Context<'_>) -> Poll<String> { +/// Poll::Ready("Hello, World!".into()) +/// } +/// +/// let read_future = poll_fn(read_line); +/// assert_eq!(read_future.await, "Hello, World!".to_owned()); +/// # } +/// ``` +#[stable(feature = "future_poll_fn", since = "1.64.0")] +pub fn poll_fn<T, F>(f: F) -> PollFn<F> +where + F: FnMut(&mut Context<'_>) -> Poll<T>, +{ + PollFn { f } +} + +/// A Future that wraps a function returning [`Poll`]. +/// +/// This `struct` is created by [`poll_fn()`]. See its +/// documentation for more. +#[must_use = "futures do nothing unless you `.await` or poll them"] +#[stable(feature = "future_poll_fn", since = "1.64.0")] +pub struct PollFn<F> { + f: F, +} + +#[stable(feature = "future_poll_fn", since = "1.64.0")] +impl<F> Unpin for PollFn<F> {} + +#[stable(feature = "future_poll_fn", since = "1.64.0")] +impl<F> fmt::Debug for PollFn<F> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("PollFn").finish() + } +} + +#[stable(feature = "future_poll_fn", since = "1.64.0")] +impl<T, F> Future for PollFn<F> +where + F: FnMut(&mut Context<'_>) -> Poll<T>, +{ + type Output = T; + + fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> { + (&mut self.f)(cx) + } +} |