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//! Definition of the `PollFn` adapter combinator use futures_core::{Future, Poll}; use futures_core::task; /// A future which adapts a function returning `Poll`. /// /// Created by the `poll_fn` function. #[derive(Debug)] #[must_use = "futures do nothing unless polled"] pub struct PollFn<F> { inner: F, } /// Creates a new future wrapping around a function returning `Poll`. /// /// Polling the returned future delegates to the wrapped function. /// /// # Examples /// /// ``` /// # extern crate futures; /// use futures::prelude::*; /// use futures::future::poll_fn; /// use futures::never::Never; /// use futures::task; /// /// # fn main() { /// fn read_line(cx: &mut task::Context) -> Poll<String, Never> { /// Ok(Async::Ready("Hello, World!".into())) /// } /// /// let read_future = poll_fn(read_line); /// # } /// ``` pub fn poll_fn<T, E, F>(f: F) -> PollFn<F> where F: FnMut(&mut task::Context) -> Poll<T, E> { PollFn { inner: f } } impl<T, E, F> Future for PollFn<F> where F: FnMut(&mut task::Context) -> Poll<T, E> { type Item = T; type Error = E; fn poll(&mut self, cx: &mut task::Context) -> Poll<T, E> { (self.inner)(cx) } }