futures_util/stream/filter_map.rs
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use futures_core::{Async, Future, IntoFuture, Poll, Stream};
use futures_core::task;
use futures_sink::{Sink};
/// 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<S, R, F>
where S: Stream,
F: FnMut(S::Item) -> R,
R: IntoFuture<Error=S::Error>,
{
stream: S,
f: F,
pending: Option<R::Future>,
}
pub fn new<S, R, F>(s: S, f: F) -> FilterMap<S, R, F>
where S: Stream,
F: FnMut(S::Item) -> R,
R: IntoFuture<Error=S::Error>,
{
FilterMap {
stream: s,
f: f,
pending: None,
}
}
impl<S, R, F> FilterMap<S, R, F>
where S: Stream,
F: FnMut(S::Item) -> R,
R: IntoFuture<Error=S::Error>,
{
/// Acquires a reference to the underlying stream that this combinator is
/// pulling from.
pub fn get_ref(&self) -> &S {
&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 S {
&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) -> S {
self.stream
}
}
// 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);
}
impl<S, R, F, B> Stream for FilterMap<S, R, F>
where S: Stream,
F: FnMut(S::Item) -> R,
R: IntoFuture<Item=Option<B>, Error=S::Error>,
{
type Item = B;
type Error = S::Error;
fn poll_next(&mut self, cx: &mut task::Context) -> Poll<Option<B>, S::Error> {
loop {
if self.pending.is_none() {
let item = match try_ready!(self.stream.poll_next(cx)) {
Some(e) => e,
None => return Ok(Async::Ready(None)),
};
let fut = ((self.f)(item)).into_future();
self.pending = Some(fut);
}
match self.pending.as_mut().unwrap().poll(cx) {
x @ Ok(Async::Ready(Some(_))) => {
self.pending = None;
return x
}
Ok(Async::Ready(None)) => self.pending = None,
Ok(Async::Pending) => return Ok(Async::Pending),
Err(e) => {
self.pending = None;
return Err(e)
}
}
}
}
}