blob: e327a3c1760f15330cd5888cd8b226d58e82f653 [file] [log] [blame]
//! Definition of the `PollFn` combinator
use core::marker::Unpin;
use core::pin::PinMut;
use futures_core::stream::Stream;
use futures_core::task::{self, Poll};
/// A stream which adapts a function returning `Poll`.
///
/// Created by the `poll_fn` function.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct PollFn<F> {
f: F,
}
impl<F> Unpin for PollFn<F> {}
/// Creates a new stream wrapping around a function returning `Poll`.
///
/// Polling the returned stream delegates to the wrapped function.
///
/// # Examples
///
/// ```
/// #![feature(futures_api)]
/// use futures::stream::poll_fn;
/// use futures::task::Poll;
///
/// let mut counter = 1usize;
///
/// let read_stream = poll_fn(move |_| -> Poll<Option<String>> {
/// if counter == 0 { return Poll::Ready(None); }
/// counter -= 1;
/// Poll::Ready(Some("Hello, World!".to_owned()))
/// });
/// ```
pub fn poll_fn<T, F>(f: F) -> PollFn<F>
where
F: FnMut(&mut task::Context) -> Poll<Option<T>>,
{
PollFn { f }
}
impl<T, F> Stream for PollFn<F>
where
F: FnMut(&mut task::Context) -> Poll<Option<T>>,
{
type Item = T;
fn poll_next(mut self: PinMut<Self>, cx: &mut task::Context) -> Poll<Option<T>> {
(&mut self.f)(cx)
}
}