blob: 8d4ef6271619b0d7f107271993c3aa135b1a64d3 [file] [log] [blame]
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::future::Future;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A stream combinator which skips elements of a stream while a predicate
/// holds.
///
/// This structure is produced by the `Stream::skip_while` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct SkipWhile<St, Fut, F> where St: Stream {
stream: St,
f: F,
pending_fut: Option<Fut>,
pending_item: Option<St::Item>,
done_skipping: bool,
}
impl<St: Unpin + Stream, Fut: Unpin, F> Unpin for SkipWhile<St, Fut, F> {}
impl<St, Fut, F> SkipWhile<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_skipping: bool);
pub(super) fn new(stream: St, f: F) -> SkipWhile<St, Fut, F> {
SkipWhile {
stream,
f,
pending_fut: None,
pending_item: None,
done_skipping: 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: Stream + FusedStream, Fut, F> FusedStream for SkipWhile<St, Fut, F> {
fn is_terminated(&self) -> bool {
self.stream.is_terminated()
}
}
impl<St, Fut, F> Stream for SkipWhile<St, Fut, F>
where St: Stream,
F: FnMut(&St::Item) -> Fut,
Fut: Future<Output = bool>,
{
type Item = St::Item;
fn poll_next(
mut self: Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Option<St::Item>> {
if self.done_skipping {
return self.as_mut().stream().poll_next(lw);
}
loop {
if self.pending_item.is_none() {
let item = match ready!(self.as_mut().stream().poll_next(lw)) {
Some(e) => e,
None => return Poll::Ready(None),
};
let fut = (self.as_mut().f())(&item);
self.as_mut().pending_fut().set(Some(fut));
*self.as_mut().pending_item() = Some(item);
}
let skipped = ready!(self.as_mut().pending_fut().as_pin_mut().unwrap().poll(lw));
let item = self.as_mut().pending_item().take().unwrap();
self.as_mut().pending_fut().set(None);
if !skipped {
*self.as_mut().done_skipping() = true;
return Poll::Ready(Some(item))
}
}
}
}
/* TODO
// Forwarding impl of Sink from the underlying stream
impl<S, R, P> Sink for SkipWhile<S, R, P>
where S: Sink + Stream, R: IntoFuture
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
delegate_sink!(stream);
}
*/