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use core::fmt;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::ready;
use futures_core::stream::{Stream, FusedStream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_project_lite::pin_project;
pin_project! {
#[must_use = "streams do nothing unless polled"]
pub struct TakeWhile<St: Stream, Fut, F> {
#[pin]
stream: St,
f: F,
#[pin]
pending_fut: Option<Fut>,
pending_item: Option<St::Item>,
done_taking: bool,
}
}
impl<St, Fut, F> fmt::Debug for TakeWhile<St, Fut, F>
where
St: Stream + fmt::Debug,
St::Item: fmt::Debug,
Fut: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TakeWhile")
.field("stream", &self.stream)
.field("pending_fut", &self.pending_fut)
.field("pending_item", &self.pending_item)
.field("done_taking", &self.done_taking)
.finish()
}
}
impl<St, Fut, F> TakeWhile<St, Fut, F>
where St: Stream,
F: FnMut(&St::Item) -> Fut,
Fut: Future<Output = bool>,
{
pub(super) fn new(stream: St, f: F) -> Self {
Self {
stream,
f,
pending_fut: None,
pending_item: None,
done_taking: false,
}
}
delegate_access_inner!(stream, St, ());
}
impl<St, Fut, F> Stream for TakeWhile<St, Fut, F>
where St: Stream,
F: FnMut(&St::Item) -> Fut,
Fut: Future<Output = bool>,
{
type Item = St::Item;
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<St::Item>> {
if self.done_taking {
return Poll::Ready(None);
}
let mut this = self.project();
Poll::Ready(loop {
if let Some(fut) = this.pending_fut.as_mut().as_pin_mut() {
let take = ready!(fut.poll(cx));
let item = this.pending_item.take();
this.pending_fut.set(None);
if take {
break item;
} else {
*this.done_taking = true;
break None;
}
} else if let Some(item) = ready!(this.stream.as_mut().poll_next(cx)) {
this.pending_fut.set(Some((this.f)(&item)));
*this.pending_item = Some(item);
} else {
break None;
}
})
}
fn size_hint(&self) -> (usize, Option<usize>) {
if self.done_taking {
return (0, Some(0));
}
let pending_len = if self.pending_item.is_some() { 1 } else { 0 };
let (_, upper) = self.stream.size_hint();
let upper = match upper {
Some(x) => x.checked_add(pending_len),
None => None,
};
(0, upper)
}
}
impl<St, Fut, F> FusedStream for TakeWhile<St, Fut, F>
where St: FusedStream,
F: FnMut(&St::Item) -> Fut,
Fut: Future<Output = bool>,
{
fn is_terminated(&self) -> bool {
self.done_taking || self.pending_item.is_none() && self.stream.is_terminated()
}
}
#[cfg(feature = "sink")]
impl<S, Fut, F, Item> Sink<Item> for TakeWhile<S, Fut, F>
where S: Stream + Sink<Item>,
{
type Error = S::Error;
delegate_sink!(stream, Item);
}