futures_util/stream/try_stream/
try_filter_map.rsuse core::fmt;
use core::pin::Pin;
use futures_core::future::TryFuture;
use futures_core::ready;
use futures_core::stream::{FusedStream, Stream, TryStream};
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 TryFilterMap<St, Fut, F> {
#[pin]
stream: St,
f: F,
#[pin]
pending: Option<Fut>,
}
}
impl<St, Fut, F> fmt::Debug for TryFilterMap<St, Fut, F>
where
St: fmt::Debug,
Fut: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("TryFilterMap")
.field("stream", &self.stream)
.field("pending", &self.pending)
.finish()
}
}
impl<St, Fut, F> TryFilterMap<St, Fut, F> {
pub(super) fn new(stream: St, f: F) -> Self {
Self { stream, f, pending: None }
}
delegate_access_inner!(stream, St, ());
}
impl<St, Fut, F, T> FusedStream for TryFilterMap<St, Fut, F>
where
St: TryStream + FusedStream,
Fut: TryFuture<Ok = Option<T>, Error = St::Error>,
F: FnMut(St::Ok) -> Fut,
{
fn is_terminated(&self) -> bool {
self.pending.is_none() && self.stream.is_terminated()
}
}
impl<St, Fut, F, T> Stream for TryFilterMap<St, Fut, F>
where
St: TryStream,
Fut: TryFuture<Ok = Option<T>, Error = St::Error>,
F: FnMut(St::Ok) -> Fut,
{
type Item = Result<T, St::Error>;
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
let mut this = self.project();
Poll::Ready(loop {
if let Some(p) = this.pending.as_mut().as_pin_mut() {
let res = ready!(p.try_poll(cx));
this.pending.set(None);
let item = res?;
if item.is_some() {
break item.map(Ok);
}
} else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
this.pending.set(Some((this.f)(item)));
} else {
break None;
}
})
}
fn size_hint(&self) -> (usize, Option<usize>) {
let pending_len = usize::from(self.pending.is_some());
let (_, upper) = self.stream.size_hint();
let upper = match upper {
Some(x) => x.checked_add(pending_len),
None => None,
};
(0, upper) }
}
#[cfg(feature = "sink")]
impl<S, Fut, F, Item> Sink<Item> for TryFilterMap<S, Fut, F>
where
S: Sink<Item>,
{
type Error = S::Error;
delegate_sink!(stream, Item);
}