futures_util/stream/
take_while.rs

1use futures_core::{Async, Poll, IntoFuture, Future, Stream};
2use futures_core::task;
3use futures_sink::{ Sink};
4
5/// A stream combinator which takes elements from a stream while a predicate
6/// holds.
7///
8/// This structure is produced by the `Stream::take_while` method.
9#[derive(Debug)]
10#[must_use = "streams do nothing unless polled"]
11pub struct TakeWhile<S, R, P> where S: Stream, R: IntoFuture {
12    stream: S,
13    pred: P,
14    pending: Option<(R::Future, S::Item)>,
15    done_taking: bool,
16}
17
18pub fn new<S, R, P>(s: S, p: P) -> TakeWhile<S, R, P>
19    where S: Stream,
20          P: FnMut(&S::Item) -> R,
21          R: IntoFuture<Item=bool, Error=S::Error>,
22{
23    TakeWhile {
24        stream: s,
25        pred: p,
26        pending: None,
27        done_taking: false,
28    }
29}
30
31impl<S, R, P> TakeWhile<S, R, P> where S: Stream, R: IntoFuture {
32    /// Acquires a reference to the underlying stream that this combinator is
33    /// pulling from.
34    pub fn get_ref(&self) -> &S {
35        &self.stream
36    }
37
38    /// Acquires a mutable reference to the underlying stream that this
39    /// combinator is pulling from.
40    ///
41    /// Note that care must be taken to avoid tampering with the state of the
42    /// stream which may otherwise confuse this combinator.
43    pub fn get_mut(&mut self) -> &mut S {
44        &mut self.stream
45    }
46
47    /// Consumes this combinator, returning the underlying stream.
48    ///
49    /// Note that this may discard intermediate state of this combinator, so
50    /// care should be taken to avoid losing resources when this is called.
51    pub fn into_inner(self) -> S {
52        self.stream
53    }
54}
55
56// Forwarding impl of Sink from the underlying stream
57impl<S, R, P> Sink for TakeWhile<S, R, P>
58    where S: Sink + Stream, R: IntoFuture
59{
60    type SinkItem = S::SinkItem;
61    type SinkError = S::SinkError;
62
63    delegate_sink!(stream);
64}
65
66impl<S, R, P> Stream for TakeWhile<S, R, P>
67    where S: Stream,
68          P: FnMut(&S::Item) -> R,
69          R: IntoFuture<Item=bool, Error=S::Error>,
70{
71    type Item = S::Item;
72    type Error = S::Error;
73
74    fn poll_next(&mut self, cx: &mut task::Context) -> Poll<Option<S::Item>, S::Error> {
75        if self.done_taking {
76            return Ok(Async::Ready(None));
77        }
78
79        if self.pending.is_none() {
80            let item = match try_ready!(self.stream.poll_next(cx)) {
81                Some(e) => e,
82                None => return Ok(Async::Ready(None)),
83            };
84            self.pending = Some(((self.pred)(&item).into_future(), item));
85        }
86
87        assert!(self.pending.is_some());
88        match self.pending.as_mut().unwrap().0.poll(cx) {
89            Ok(Async::Ready(true)) => {
90                let (_, item) = self.pending.take().unwrap();
91                Ok(Async::Ready(Some(item)))
92            },
93            Ok(Async::Ready(false)) => {
94                self.done_taking = true;
95                self.pending = None;
96                Ok(Async::Ready(None))
97            }
98            Ok(Async::Pending) => Ok(Async::Pending),
99            Err(e) => {
100                self.pending = None;
101                Err(e)
102            }
103        }
104    }
105}
futures_util/stream/take_while.rs

futures_util/stream/
take_while.rs
