pending.rs.html -- source
Description: Source to the Rust file `library/core/src/future/pending.rs`.
Keywords: rust, rustlang, rust-lang

     1
     2
     3
     4
     5
     6
     7
     8
     9
    10
    11
    12
    13
    14
    15
    16
    17
    18
    19
    20
    21
    22
    23
    24
    25
    26
    27
    28
    29
    30
    31
    32
    33
    34
    35
    36
    37
    38
    39
    40
    41
    42
    43
    44
    45
    46
    47
    48
    49
    50
    51
    52
    53
    54
    55
    56
    57
    58
    59
    60
    61

    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<T>,
    }

    /// Creates a future which never resolves, representing a computation that never
    /// finishes.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use core::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> Unpin for Pending<T> {}

    #[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()
        }
    }