blob: a7939ce65275c2a1bf9cf9cfe63e1ee1cb846c34 [file] [log] [blame]
use core::marker::Unpin;
use core::pin::PinMut;
use futures_core::future::Future;
use futures_core::stream::Stream;
use futures_core::task::{self, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A stream combinator which takes elements from a stream while a predicate
/// holds.
///
/// This structure is produced by the `Stream::take_while` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct TakeWhile<St: Stream , Fut, F> {
stream: St,
f: F,
pending_fut: Option<Fut>,
pending_item: Option<St::Item>,
done_taking: bool,
}
impl<St: Unpin + Stream, Fut: Unpin, F> Unpin for TakeWhile<St, Fut, F> {}
impl<St, Fut, F> TakeWhile<St, Fut, F>
where St: Stream,
F: FnMut(&St::Item) -> Fut,
Fut: Future<Output = bool>,
{
unsafe_pinned!(stream: St);
unsafe_unpinned!(f: F);
unsafe_pinned!(pending_fut: Option<Fut>);
unsafe_unpinned!(pending_item: Option<St::Item>);
unsafe_unpinned!(done_taking: bool);
pub(super) fn new(stream: St, f: F) -> TakeWhile<St, Fut, F> {
TakeWhile {
stream,
f,
pending_fut: None,
pending_item: None,
done_taking: false,
}
}
/// Acquires a reference to the underlying stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &St {
&self.stream
}
/// Acquires a mutable reference to the underlying stream that this
/// combinator is pulling from.
///
/// Note that care must be taken to avoid tampering with the state of the
/// stream which may otherwise confuse this combinator.
pub fn get_mut(&mut self) -> &mut St {
&mut self.stream
}
/// Consumes this combinator, returning the underlying stream.
///
/// Note that this may discard intermediate state of this combinator, so
/// care should be taken to avoid losing resources when this is called.
pub fn into_inner(self) -> St {
self.stream
}
}
impl<St, Fut, F> Stream for TakeWhile<St, Fut, F>
where St: Stream,
F: FnMut(&St::Item) -> Fut,
Fut: Future<Output = bool>,
{
type Item = St::Item;
fn poll_next(
mut self: PinMut<Self>,
cx: &mut task::Context,
) -> Poll<Option<St::Item>> {
if *self.done_taking() {
return Poll::Ready(None);
}
if self.pending_item().is_none() {
let item = match ready!(self.stream().poll_next(cx)) {
Some(e) => e,
None => return Poll::Ready(None),
};
let fut = (self.f())(&item);
PinMut::set(self.pending_fut(), Some(fut));
*self.pending_item() = Some(item);
}
let take = ready!(self.pending_fut().as_pin_mut().unwrap().poll(cx));
PinMut::set(self.pending_fut(), None);
let item = self.pending_item().take().unwrap();
if take {
Poll::Ready(Some(item))
} else {
*self.done_taking() = true;
Poll::Ready(None)
}
}
}
/* TODO
// Forwarding impl of Sink from the underlying stream
impl<S, R, P> Sink for TakeWhile<S, R, P>
where S: Sink + Stream, R: IntoFuture
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
delegate_sink!(stream);
}
*/