blob: 35d2c57190d340f138b5e8576497bbdf26777f8a [file] [log] [blame]
use core::marker::Unpin;
use core::mem::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 combinator used to filter the results of a stream and simultaneously map
/// them to a different type.
///
/// This structure is returned by the `Stream::filter_map` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct FilterMap<St, Fut, F>
where St: Stream,
F: FnMut(St::Item) -> Fut,
Fut: Future,
{
stream: St,
f: F,
pending: Option<Fut>,
}
impl<St, Fut, F> Unpin for FilterMap<St, Fut, F>
where St: Stream + Unpin,
F: FnMut(St::Item) -> Fut,
Fut: Future + Unpin,
{}
impl<St, Fut, F> FilterMap<St, Fut, F>
where St: Stream,
F: FnMut(St::Item) -> Fut,
Fut: Future,
{
unsafe_pinned!(stream: St);
unsafe_unpinned!(f: F);
unsafe_pinned!(pending: Option<Fut>);
pub(super) fn new(stream: St, f: F) -> FilterMap<St, Fut, F> {
FilterMap { stream, f, pending: None }
}
/// 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, T> Stream for FilterMap<St, Fut, F>
where St: Stream,
F: FnMut(St::Item) -> Fut,
Fut: Future<Output = Option<T>>,
{
type Item = T;
fn poll_next(
mut self: PinMut<Self>,
cx: &mut task::Context,
) -> Poll<Option<T>> {
loop {
if self.pending().as_pin_mut().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(), Some(fut));
}
let item = ready!(self.pending().as_pin_mut().unwrap().poll(cx));
PinMut::set(self.pending(), None);
if item.is_some() {
return Poll::Ready(item);
}
}
}
}
/* TODO
// Forwarding impl of Sink from the underlying stream
impl<S, R, F> Sink for FilterMap<S, R, F>
where S: Stream + Sink,
F: FnMut(S::Item) -> R,
R: IntoFuture<Error=S::Error>,
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
delegate_sink!(stream);
}
*/