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use core::fmt;
use core::pin::Pin;
use futures_core::future::TryFuture;
use futures_core::ready;
use futures_core::stream::{Stream, TryStream, FusedStream};
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 AndThen<St, Fut, F> {
#[pin]
stream: St,
#[pin]
future: Option<Fut>,
f: F,
}
}
impl<St, Fut, F> fmt::Debug for AndThen<St, Fut, F>
where
St: fmt::Debug,
Fut: fmt::Debug,
{
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
f.debug_struct("AndThen")
.field("stream", &self.stream)
.field("future", &self.future)
.finish()
}
}
impl<St, Fut, F> AndThen<St, Fut, F>
where St: TryStream,
F: FnMut(St::Ok) -> Fut,
Fut: TryFuture<Error = St::Error>,
{
pub(super) fn new(stream: St, f: F) -> Self {
Self { stream, future: None, f }
}
delegate_access_inner!(stream, St, ());
}
impl<St, Fut, F> Stream for AndThen<St, Fut, F>
where St: TryStream,
F: FnMut(St::Ok) -> Fut,
Fut: TryFuture<Error = St::Error>,
{
type Item = Result<Fut::Ok, 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(fut) = this.future.as_mut().as_pin_mut() {
let item = ready!(fut.try_poll(cx));
this.future.set(None);
break Some(item);
} else if let Some(item) = ready!(this.stream.as_mut().try_poll_next(cx)?) {
this.future.set(Some((this.f)(item)));
} else {
break None;
}
})
}
fn size_hint(&self) -> (usize, Option<usize>) {
let future_len = if self.future.is_some() { 1 } else { 0 };
let (lower, upper) = self.stream.size_hint();
let lower = lower.saturating_add(future_len);
let upper = match upper {
Some(x) => x.checked_add(future_len),
None => None,
};
(lower, upper)
}
}
impl<St, Fut, F> FusedStream for AndThen<St, Fut, F>
where St: TryStream + FusedStream,
F: FnMut(St::Ok) -> Fut,
Fut: TryFuture<Error = St::Error>,
{
fn is_terminated(&self) -> bool {
self.future.is_none() && self.stream.is_terminated()
}
}
#[cfg(feature = "sink")]
impl<S, Fut, F, Item> Sink<Item> for AndThen<S, Fut, F>
where S: Sink<Item>,
{
type Error = S::Error;
delegate_sink!(stream, Item);
}