blob: f0367a36242b455dce0d1a76c3c07aa13a03c79b [file] [log] [blame]
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A stream combinator which chains a computation onto each item produced by a
/// stream.
///
/// This structure is produced by the `Stream::then` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Then<St, Fut, F> {
stream: St,
future: Option<Fut>,
f: F,
}
impl<St: Unpin, Fut: Unpin, F> Unpin for Then<St, Fut, F> {}
impl<St, Fut, F> Then<St, Fut, F>
where St: Stream,
F: FnMut(St::Item) -> Fut,
{
unsafe_pinned!(stream: St);
unsafe_pinned!(future: Option<Fut>);
unsafe_unpinned!(f: F);
pub(super) fn new(stream: St, f: F) -> Then<St, Fut, F> {
Then {
stream,
future: None,
f,
}
}
}
impl<St: FusedStream, Fut, F> FusedStream for Then<St, Fut, F> {
fn is_terminated(&self) -> bool {
self.future.is_none() && self.stream.is_terminated()
}
}
impl<St, Fut, F> Stream for Then<St, Fut, F>
where St: Stream,
F: FnMut(St::Item) -> Fut,
Fut: Future,
{
type Item = Fut::Output;
fn poll_next(
mut self: Pin<&mut Self>,
lw: &LocalWaker
) -> Poll<Option<Fut::Output>> {
if self.as_mut().future().as_pin_mut().is_none() {
let item = match ready!(self.as_mut().stream().poll_next(lw)) {
None => return Poll::Ready(None),
Some(e) => e,
};
let fut = (self.as_mut().f())(item);
self.as_mut().future().set(Some(fut));
}
let e = ready!(self.as_mut().future().as_pin_mut().unwrap().poll(lw));
self.as_mut().future().set(None);
Poll::Ready(Some(e))
}
}
/* TODO
// Forwarding impl of Sink from the underlying stream
impl<S, U, F> Sink for Then<S, U, F>
where S: Sink, U: IntoFuture,
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
delegate_sink!(stream);
}
*/