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//! Definition of the `PollFn` combinator use {Stream, 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> { inner: F, } /// Creates a new stream wrapping around a function returning `Poll`. /// /// Polling the returned stream delegates to the wrapped function. /// /// # Examples /// /// ``` /// use futures::stream::poll_fn; /// use futures::{Async, Poll}; /// /// let mut counter = 1usize; /// /// let read_stream = poll_fn(move || -> Poll<Option<String>, std::io::Error> { /// if counter == 0 { return Ok(Async::Ready(None)); } /// counter -= 1; /// Ok(Async::Ready(Some("Hello, World!".to_owned()))) /// }); /// ``` pub fn poll_fn<T, E, F>(f: F) -> PollFn<F> where F: FnMut() -> Poll<Option<T>, E>, { PollFn { inner: f } } impl<T, E, F> Stream for PollFn<F> where F: FnMut() -> Poll<Option<T>, E>, { type Item = T; type Error = E; fn poll(&mut self) -> Poll<Option<T>, E> { (self.inner)() } }