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use crate::Stream;
use core::fmt;
use core::pin::Pin;
use core::task::{Context, Poll};
use pin_project_lite::pin_project;
pin_project! {
/// Stream for the [`take_while`](super::StreamExt::take_while) method.
#[must_use = "streams do nothing unless polled"]
pub struct TakeWhile<St, F> {
#[pin]
stream: St,
predicate: F,
done: bool,
}
}
impl<St, F> fmt::Debug for TakeWhile<St, F>
where
St: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TakeWhile")
.field("stream", &self.stream)
.field("done", &self.done)
.finish()
}
}
impl<St, F> TakeWhile<St, F> {
pub(super) fn new(stream: St, predicate: F) -> Self {
Self {
stream,
predicate,
done: false,
}
}
}
impl<St, F> Stream for TakeWhile<St, F>
where
St: Stream,
F: FnMut(&St::Item) -> bool,
{
type Item = St::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
if !*self.as_mut().project().done {
self.as_mut().project().stream.poll_next(cx).map(|ready| {
let ready = ready.and_then(|item| {
if !(self.as_mut().project().predicate)(&item) {
None
} else {
Some(item)
}
});
if ready.is_none() {
*self.as_mut().project().done = true;
}
ready
})
} else {
Poll::Ready(None)
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
if self.done {
return (0, Some(0));
}
let (_, upper) = self.stream.size_hint();
(0, upper)
}
}