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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 [`map_while`](super::StreamExt::map_while) method.
#[must_use = "streams do nothing unless polled"]
pub struct MapWhile<St, F> {
#[pin]
stream: St,
f: F,
}
}
impl<St, F> fmt::Debug for MapWhile<St, F>
where
St: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("MapWhile")
.field("stream", &self.stream)
.finish()
}
}
impl<St, F> MapWhile<St, F> {
pub(super) fn new(stream: St, f: F) -> Self {
MapWhile { stream, f }
}
}
impl<St, F, T> Stream for MapWhile<St, F>
where
St: Stream,
F: FnMut(St::Item) -> Option<T>,
{
type Item = T;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<T>> {
let me = self.project();
let f = me.f;
me.stream.poll_next(cx).map(|opt| opt.and_then(f))
}
fn size_hint(&self) -> (usize, Option<usize>) {
let (_, upper) = self.stream.size_hint();
(0, upper)
}
}