84 lines
2.1 KiB
Rust
84 lines
2.1 KiB
Rust
use crate::Stream;
|
|
|
|
use core::fmt;
|
|
use core::future::Future;
|
|
use core::pin::Pin;
|
|
use core::task::{Context, Poll};
|
|
use pin_project_lite::pin_project;
|
|
|
|
pin_project! {
|
|
/// Stream for the [`then`](super::StreamExt::then) method.
|
|
#[must_use = "streams do nothing unless polled"]
|
|
pub struct Then<St, Fut, F> {
|
|
#[pin]
|
|
stream: St,
|
|
#[pin]
|
|
future: Option<Fut>,
|
|
f: F,
|
|
}
|
|
}
|
|
|
|
impl<St, Fut, F> fmt::Debug for Then<St, Fut, F>
|
|
where
|
|
St: fmt::Debug,
|
|
{
|
|
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
|
|
f.debug_struct("Then")
|
|
.field("stream", &self.stream)
|
|
.finish()
|
|
}
|
|
}
|
|
|
|
impl<St, Fut, F> Then<St, Fut, F> {
|
|
pub(super) fn new(stream: St, f: F) -> Self {
|
|
Then {
|
|
stream,
|
|
future: None,
|
|
f,
|
|
}
|
|
}
|
|
}
|
|
|
|
impl<St, F, Fut> Stream for Then<St, Fut, F>
|
|
where
|
|
St: Stream,
|
|
Fut: Future,
|
|
F: FnMut(St::Item) -> Fut,
|
|
{
|
|
type Item = Fut::Output;
|
|
|
|
fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Fut::Output>> {
|
|
let mut me = self.project();
|
|
|
|
loop {
|
|
if let Some(future) = me.future.as_mut().as_pin_mut() {
|
|
match future.poll(cx) {
|
|
Poll::Ready(item) => {
|
|
me.future.set(None);
|
|
return Poll::Ready(Some(item));
|
|
}
|
|
Poll::Pending => return Poll::Pending,
|
|
}
|
|
}
|
|
|
|
match me.stream.as_mut().poll_next(cx) {
|
|
Poll::Ready(Some(item)) => {
|
|
me.future.set(Some((me.f)(item)));
|
|
}
|
|
Poll::Ready(None) => return Poll::Ready(None),
|
|
Poll::Pending => return Poll::Pending,
|
|
}
|
|
}
|
|
}
|
|
|
|
fn size_hint(&self) -> (usize, Option<usize>) {
|
|
let future_len = usize::from(self.future.is_some());
|
|
let (lower, upper) = self.stream.size_hint();
|
|
|
|
let lower = lower.saturating_add(future_len);
|
|
let upper = upper.and_then(|upper| upper.checked_add(future_len));
|
|
|
|
(lower, upper)
|
|
}
|
|
}
|