blob: 24fb327bd658d444aaf5898c7cb30d6f69c5a7c2 [file] [log] [blame]
use {Poll, Async};
use stream::Stream;
/// A stream which emits single element and then EOF.
///
/// This stream will never block and is always ready.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Once<T, E>(Option<Result<T, E>>);
/// Creates a stream of single element
///
/// ```rust
/// use futures::*;
///
/// let mut stream = stream::once::<(), _>(Err(17));
/// assert_eq!(Err(17), stream.poll());
/// assert_eq!(Ok(Async::Ready(None)), stream.poll());
/// ```
pub fn once<T, E>(item: Result<T, E>) -> Once<T, E> {
Once(Some(item))
}
impl<T, E> Stream for Once<T, E> {
type Item = T;
type Error = E;
fn poll(&mut self) -> Poll<Option<T>, E> {
match self.0.take() {
Some(Ok(e)) => Ok(Async::Ready(Some(e))),
Some(Err(e)) => Err(e),
None => Ok(Async::Ready(None)),
}
}
}