1 | //! Definition of the `PollFn` adapter combinator |
2 | |
3 | use super::assert_future; |
4 | use core::fmt; |
5 | use core::pin::Pin; |
6 | use futures_core::future::Future; |
7 | use futures_core::task::{Context, Poll}; |
8 | |
9 | /// Future for the [`poll_fn`] function. |
10 | #[must_use = "futures do nothing unless you `.await` or poll them" ] |
11 | pub struct PollFn<F> { |
12 | f: F, |
13 | } |
14 | |
15 | impl<F> Unpin for PollFn<F> {} |
16 | |
17 | /// Creates a new future wrapping around a function returning [`Poll`]. |
18 | /// |
19 | /// Polling the returned future delegates to the wrapped function. |
20 | /// |
21 | /// # Examples |
22 | /// |
23 | /// ``` |
24 | /// # futures::executor::block_on(async { |
25 | /// use futures::future::poll_fn; |
26 | /// use futures::task::{Context, Poll}; |
27 | /// |
28 | /// fn read_line(_cx: &mut Context<'_>) -> Poll<String> { |
29 | /// Poll::Ready("Hello, World!" .into()) |
30 | /// } |
31 | /// |
32 | /// let read_future = poll_fn(read_line); |
33 | /// assert_eq!(read_future.await, "Hello, World!" .to_owned()); |
34 | /// # }); |
35 | /// ``` |
36 | pub fn poll_fn<T, F>(f: F) -> PollFn<F> |
37 | where |
38 | F: FnMut(&mut Context<'_>) -> Poll<T>, |
39 | { |
40 | assert_future::<T, _>(PollFn { f }) |
41 | } |
42 | |
43 | impl<F> fmt::Debug for PollFn<F> { |
44 | fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { |
45 | f.debug_struct(name:"PollFn" ).finish() |
46 | } |
47 | } |
48 | |
49 | impl<T, F> Future for PollFn<F> |
50 | where |
51 | F: FnMut(&mut Context<'_>) -> Poll<T>, |
52 | { |
53 | type Output = T; |
54 | |
55 | fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> { |
56 | (&mut self.f)(cx) |
57 | } |
58 | } |
59 | |