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//! Definition of the `PollFn` adapter combinator use core::marker::Unpin; use core::pin::Pin; use futures_core::future::Future; use futures_core::task::{LocalWaker, Poll}; /// A future which wraps a function returning [`Poll`]. /// /// Created by the [`poll_fn()`] function. #[derive(Debug)] #[must_use = "futures do nothing unless polled"] pub struct PollFn<F> { f: F, } impl<F> Unpin for PollFn<F> {} /// Creates a new future wrapping around a function returning [`Poll`]. /// /// Polling the returned future delegates to the wrapped function. /// /// # Examples /// /// ``` /// #![feature(async_await, await_macro, futures_api)] /// # futures::executor::block_on(async { /// use futures::future::poll_fn; /// use futures::task::{LocalWaker, Poll}; /// /// fn read_line(lw: &LocalWaker) -> Poll<String> { /// Poll::Ready("Hello, World!".into()) /// } /// /// let read_future = poll_fn(read_line); /// assert_eq!(await!(read_future), "Hello, World!".to_owned()); /// # }); /// ``` pub fn poll_fn<T, F>(f: F) -> PollFn<F> where F: FnMut(&LocalWaker) -> Poll<T> { PollFn { f } } impl<T, F> Future for PollFn<F> where F: FnMut(&LocalWaker) -> Poll<T>, { type Output = T; fn poll(mut self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<T> { (&mut self.f)(lw) } }