diff --git a/src/libcore/future/mod.rs b/src/libcore/future/mod.rs index 2555d91ae8d9a..6d1ad9db74435 100644 --- a/src/libcore/future/mod.rs +++ b/src/libcore/future/mod.rs @@ -12,6 +12,7 @@ use crate::{ mod future; mod into_future; mod pending; +mod poll_fn; mod ready; #[stable(feature = "futures_api", since = "1.36.0")] @@ -25,6 +26,9 @@ pub use pending::{pending, Pending}; #[unstable(feature = "future_readiness_fns", issue = "70921")] pub use ready::{ready, Ready}; +#[unstable(feature = "future_poll_fn", issue = "72302")] +pub use poll_fn::{poll_fn, PollFn}; + /// This type is needed because: /// /// a) Generators cannot implement `for<'a, 'b> Generator<&'a mut Context<'b>>`, so we need to pass diff --git a/src/libcore/future/poll_fn.rs b/src/libcore/future/poll_fn.rs new file mode 100644 index 0000000000000..9ab3bfcea1c71 --- /dev/null +++ b/src/libcore/future/poll_fn.rs @@ -0,0 +1,66 @@ +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 +/// +/// ``` +/// #![feature(future_poll_fn)] +/// # async fn run() { +/// use core::future::poll_fn; +/// use core::task::{Context, Poll}; +/// +/// fn read_line(_cx: &mut Context<'_>) -> Poll { +/// Poll::Ready("Hello, World!".into()) +/// } +/// +/// let read_future = poll_fn(read_line); +/// assert_eq!(read_future.await, "Hello, World!".to_owned()); +/// # }; +/// ``` +#[unstable(feature = "future_poll_fn", issue = "72302")] +pub fn poll_fn(f: F) -> PollFn +where + F: FnMut(&mut Context<'_>) -> Poll, +{ + PollFn { f } +} + +/// A Future that wraps a function returning `Poll`. +/// +/// This `struct` is created by the [`poll_fn`] function. See its +/// documentation for more. +/// +/// [`poll_fn`]: fn.poll_fn.html +#[must_use = "futures do nothing unless you `.await` or poll them"] +#[unstable(feature = "future_poll_fn", issue = "72302")] +pub struct PollFn { + f: F, +} + +#[unstable(feature = "future_poll_fn", issue = "72302")] +impl Unpin for PollFn {} + +#[unstable(feature = "future_poll_fn", issue = "72302")] +impl fmt::Debug for PollFn { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("PollFn").finish() + } +} + +#[unstable(feature = "future_poll_fn", issue = "72302")] +impl Future for PollFn +where + F: FnMut(&mut Context<'_>) -> Poll, +{ + type Output = T; + + fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll { + (&mut self.f)(cx) + } +}