67 lines
1.9 KiB
Rust
67 lines
1.9 KiB
Rust
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. If the returned future is pinned, then the
|
|
/// captured environment of the wrapped function is also pinned in-place, so as long as the closure
|
|
/// does not move out of its captures it can soundly create pinned references to them.
|
|
///
|
|
/// # 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> 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(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
|
|
// SAFETY: We are not moving out of the pinned field.
|
|
(unsafe { &mut self.get_unchecked_mut().f })(cx)
|
|
}
|
|
}
|