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use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_utils::unsafe_pinned;
/// Stream for the [`flatten`](super::StreamExt::flatten) method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Flatten<St>
where
St: Stream,
{
stream: St,
next: Option<St::Item>,
}
impl<St> Unpin for Flatten<St>
where
St: Stream + Unpin,
St::Item: Unpin,
{
}
impl<St> Flatten<St>
where
St: Stream,
{
unsafe_pinned!(stream: St);
unsafe_pinned!(next: Option<St::Item>);
}
impl<St> Flatten<St>
where
St: Stream,
St::Item: Stream,
{
pub(super) fn new(stream: St) -> Self {
Self { stream, next: None }
}
/// Acquires a reference to the underlying stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &St {
&self.stream
}
/// Acquires a mutable reference to the underlying stream that this
/// combinator is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the
/// stream which may otherwise confuse this combinator.
pub fn get_mut(&mut self) -> &mut St {
&mut self.stream
}
/// Acquires a pinned mutable reference to the underlying stream that this
/// combinator is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the
/// stream which may otherwise confuse this combinator.
pub fn get_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
self.stream()
}
/// Consumes this combinator, returning the underlying stream.
///
/// Note that this may discard intermediate state of this combinator, so
/// care should be taken to avoid losing resources when this is called.
pub fn into_inner(self) -> St {
self.stream
}
}
impl<St> FusedStream for Flatten<St>
where
St: FusedStream,
St::Item: Stream,
{
fn is_terminated(&self) -> bool {
self.next.is_none() && self.stream.is_terminated()
}
}
impl<St> Stream for Flatten<St>
where
St: Stream,
St::Item: Stream,
{
type Item = <St::Item as Stream>::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
loop {
if self.next.is_none() {
match ready!(self.as_mut().stream().poll_next(cx)) {
Some(e) => self.as_mut().next().set(Some(e)),
None => return Poll::Ready(None),
}
}
if let Some(item) = ready!(self.as_mut().next().as_pin_mut().unwrap().poll_next(cx)) {
return Poll::Ready(Some(item));
} else {
self.as_mut().next().set(None);
}
}
}
}
// Forwarding impl of Sink from the underlying stream
#[cfg(feature = "sink")]
impl<S, Item> Sink<Item> for Flatten<S>
where
S: Stream + Sink<Item>,
{
type Error = S::Error;
delegate_sink!(stream, Item);
}
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