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use core::fmt;
use core::pin::Pin;
use futures_core::future::{TryFuture};
use futures_core::stream::{Stream, TryStream, FusedStream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_project::{pin_project, project};
/// Stream for the [`try_filter_map`](super::TryStreamExt::try_filter_map)
/// method.
#[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 {
TryFilterMap { 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>;
#[project]
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<Result<T, St::Error>>> {
#[project]
let TryFilterMap { mut stream, f, mut pending } = self.project();
Poll::Ready(loop {
if let Some(p) = pending.as_mut().as_pin_mut() {
// We have an item in progress, poll that until it's done
let item = ready!(p.try_poll(cx)?);
pending.set(None);
if item.is_some() {
break item.map(Ok);
}
} else if let Some(item) = ready!(stream.as_mut().try_poll_next(cx)?) {
// No item in progress, but the stream is still going
pending.set(Some(f(item)));
} else {
// The stream is done
break None;
}
})
}
fn size_hint(&self) -> (usize, Option<usize>) {
let pending_len = if self.pending.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) // can't know a lower bound, due to the predicate
}
}
// Forwarding impl of Sink from the underlying stream
#[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);
}
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