futures_util/stream/
skip_while.rs

1use futures_core::{Async, Poll, IntoFuture, Future, Stream};
2use futures_core::task;
3use futures_sink::{ Sink};
4
5/// A stream combinator which skips elements of a stream while a predicate
6/// holds.
7///
8/// This structure is produced by the `Stream::skip_while` method.
9#[derive(Debug)]
10#[must_use = "streams do nothing unless polled"]
11pub struct SkipWhile<S, R, P> where S: Stream, R: IntoFuture {
12    stream: S,
13    pred: P,
14    pending: Option<(R::Future, S::Item)>,
15    done_skipping: bool,
16}
17
18pub fn new<S, R, P>(s: S, p: P) -> SkipWhile<S, R, P>
19    where S: Stream,
20          P: FnMut(&S::Item) -> R,
21          R: IntoFuture<Item=bool, Error=S::Error>,
22{
23    SkipWhile {
24        stream: s,
25        pred: p,
26        pending: None,
27        done_skipping: false,
28    }
29}
30
31impl<S, R, P> SkipWhile<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 SkipWhile<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 SkipWhile<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_skipping {
76            return self.stream.poll_next(cx);
77        }
78
79        loop {
80            if self.pending.is_none() {
81                let item = match try_ready!(self.stream.poll_next(cx)) {
82                    Some(e) => e,
83                    None => return Ok(Async::Ready(None)),
84                };
85                self.pending = Some(((self.pred)(&item).into_future(), item));
86            }
87
88            match self.pending.as_mut().unwrap().0.poll(cx) {
89                Ok(Async::Ready(true)) => self.pending = None,
90                Ok(Async::Ready(false)) => {
91                    let (_, item) = self.pending.take().unwrap();
92                    self.done_skipping = true;
93                    return Ok(Async::Ready(Some(item)))
94                }
95                Ok(Async::Pending) => return Ok(Async::Pending),
96                Err(e) => {
97                    self.pending = None;
98                    return Err(e)
99                }
100            }
101        }
102    }
103}
futures_util/stream/skip_while.rs

futures_util/stream/
skip_while.rs
