blob: cab338e922be9c50c56aaa2ccd65d079a789da92 [file] [log] [blame]
use {Async, IntoFuture, Future, Poll};
use stream::Stream;
/// A stream combinator which chains a computation onto each item produced by a
/// stream.
///
/// This structure is produced by the `Stream::then` method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Then<S, F, U>
where U: IntoFuture,
{
stream: S,
future: Option<U::Future>,
f: F,
}
pub fn new<S, F, U>(s: S, f: F) -> Then<S, F, U>
where S: Stream,
F: FnMut(Result<S::Item, S::Error>) -> U,
U: IntoFuture,
{
Then {
stream: s,
future: None,
f: f,
}
}
// Forwarding impl of Sink from the underlying stream
impl<S, F, U> ::sink::Sink for Then<S, F, U>
where S: ::sink::Sink, U: IntoFuture,
{
type SinkItem = S::SinkItem;
type SinkError = S::SinkError;
fn start_send(&mut self, item: S::SinkItem) -> ::StartSend<S::SinkItem, S::SinkError> {
self.stream.start_send(item)
}
fn poll_complete(&mut self) -> Poll<(), S::SinkError> {
self.stream.poll_complete()
}
fn close(&mut self) -> Poll<(), S::SinkError> {
self.stream.close()
}
}
impl<S, F, U> Stream for Then<S, F, U>
where S: Stream,
F: FnMut(Result<S::Item, S::Error>) -> U,
U: IntoFuture,
{
type Item = U::Item;
type Error = U::Error;
fn poll(&mut self) -> Poll<Option<U::Item>, U::Error> {
if self.future.is_none() {
let item = match self.stream.poll() {
Ok(Async::NotReady) => return Ok(Async::NotReady),
Ok(Async::Ready(None)) => return Ok(Async::Ready(None)),
Ok(Async::Ready(Some(e))) => Ok(e),
Err(e) => Err(e),
};
self.future = Some((self.f)(item).into_future());
}
assert!(self.future.is_some());
match self.future.as_mut().unwrap().poll() {
Ok(Async::Ready(e)) => {
self.future = None;
Ok(Async::Ready(Some(e)))
}
Err(e) => {
self.future = None;
Err(e)
}
Ok(Async::NotReady) => Ok(Async::NotReady)
}
}
}