blob: b0875661aab87f291c0c26bc99c523014dab94bb [file] [log] [blame]
use core::marker::Unpin;
use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{LocalWaker, Poll};
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// A stream combinator which skips a number of elements before continuing.
///
/// This structure is produced by the `Stream::skip` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Skip<St> {
stream: St,
remaining: u64,
}
impl<St: Unpin> Unpin for Skip<St> {}
impl<St: Stream> Skip<St> {
unsafe_pinned!(stream: St);
unsafe_unpinned!(remaining: u64);
pub(super) fn new(stream: St, n: u64) -> Skip<St> {
Skip {
stream,
remaining: n,
}
}
/// 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: FusedStream> FusedStream for Skip<St> {
fn is_terminated(&self) -> bool {
self.stream.is_terminated()
}
}
impl<St: Stream> Stream for Skip<St> {
type Item = St::Item;
fn poll_next(
mut self: Pin<&mut Self>,
lw: &LocalWaker,
) -> Poll<Option<St::Item>> {
while *self.remaining() > 0 {
match ready!(self.stream().poll_next(lw)) {
Some(_) => *self.remaining() -= 1,
None => return Poll::Ready(None),
}
}
self.stream().poll_next(lw)
}
}
/* TODO
// Forwarding impl of Sink from the underlying stream
impl<S> Sink for Skip<S>
where S: Sink
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
delegate_sink!(stream);
}
*/