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use crate::stream::Stream;
use core::cmp;
use core::fmt;
use core::pin::Pin;
use core::task::{Context, Poll};
use pin_project_lite::pin_project;
pin_project! {
/// Stream for the [`map`](super::StreamExt::map) method.
#[must_use = "streams do nothing unless polled"]
pub struct Take<St> {
#[pin]
stream: St,
remaining: usize,
}
}
impl<St> fmt::Debug for Take<St>
where
St: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("Take")
.field("stream", &self.stream)
.finish()
}
}
impl<St: Stream> Take<St> {
pub(super) fn new(stream: St, remaining: usize) -> Self {
Self { stream, remaining }
}
}
impl<St> Stream for Take<St>
where
St: Stream,
{
type Item = St::Item;
fn poll_next(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
if *self.as_mut().project().remaining > 0 {
self.as_mut().project().stream.poll_next(cx).map(|ready| {
match &ready {
Some(_) => {
*self.as_mut().project().remaining -= 1;
}
None => {
*self.as_mut().project().remaining = 0;
}
}
ready
})
} else {
Poll::Ready(None)
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
if self.remaining == 0 {
return (0, Some(0));
}
let (lower, upper) = self.stream.size_hint();
let lower = cmp::min(lower, self.remaining as usize);
let upper = match upper {
Some(x) if x < self.remaining as usize => Some(x),
_ => Some(self.remaining as usize),
};
(lower, upper)
}
}
|
