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Diffstat (limited to 'library/core/src/future/pending.rs')
-rw-r--r-- | library/core/src/future/pending.rs | 58 |
1 files changed, 58 insertions, 0 deletions
diff --git a/library/core/src/future/pending.rs b/library/core/src/future/pending.rs new file mode 100644 index 000000000..2877e66ec --- /dev/null +++ b/library/core/src/future/pending.rs @@ -0,0 +1,58 @@ +use crate::fmt::{self, Debug}; +use crate::future::Future; +use crate::marker; +use crate::pin::Pin; +use crate::task::{Context, Poll}; + +/// Creates a future which never resolves, representing a computation that never +/// finishes. +/// +/// This `struct` is created by [`pending()`]. See its +/// documentation for more. +#[stable(feature = "future_readiness_fns", since = "1.48.0")] +#[must_use = "futures do nothing unless you `.await` or poll them"] +pub struct Pending<T> { + _data: marker::PhantomData<fn() -> T>, +} + +/// Creates a future which never resolves, representing a computation that never +/// finishes. +/// +/// # Examples +/// +/// ```no_run +/// use std::future; +/// +/// # async fn run() { +/// let future = future::pending(); +/// let () = future.await; +/// unreachable!(); +/// # } +/// ``` +#[stable(feature = "future_readiness_fns", since = "1.48.0")] +pub fn pending<T>() -> Pending<T> { + Pending { _data: marker::PhantomData } +} + +#[stable(feature = "future_readiness_fns", since = "1.48.0")] +impl<T> Future for Pending<T> { + type Output = T; + + fn poll(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<T> { + Poll::Pending + } +} + +#[stable(feature = "future_readiness_fns", since = "1.48.0")] +impl<T> Debug for Pending<T> { + fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { + f.debug_struct("Pending").finish() + } +} + +#[stable(feature = "future_readiness_fns", since = "1.48.0")] +impl<T> Clone for Pending<T> { + fn clone(&self) -> Self { + pending() + } +} |