forked from rust-lang/futures-rs
/
take.rs
100 lines (87 loc) · 2.68 KB
/
take.rs
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
use core::pin::Pin;
use futures_core::stream::{Stream, FusedStream};
use futures_core::task::{Context, Poll};
#[cfg(feature = "sink")]
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};
/// Stream for the [`take`](super::StreamExt::take) method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Take<St> {
stream: St,
remaining: u64,
}
impl<St: Unpin> Unpin for Take<St> {}
impl<St: Stream> Take<St> {
unsafe_pinned!(stream: St);
unsafe_unpinned!(remaining: u64);
pub(super) fn new(stream: St, n: u64) -> Take<St> {
Take {
stream,
remaining: n,
}
}
/// 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
}
/// Acquires a pinned 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_pin_mut(self: Pin<&mut Self>) -> Pin<&mut St> {
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> Stream for Take<St>
where St: Stream,
{
type Item = St::Item;
fn poll_next(
mut self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<St::Item>> {
if self.remaining == 0 {
Poll::Ready(None)
} else {
let next = ready!(self.as_mut().stream().poll_next(cx));
match next {
Some(_) => *self.as_mut().remaining() -= 1,
None => *self.as_mut().remaining() = 0,
}
Poll::Ready(next)
}
}
}
impl<St> FusedStream for Take<St>
where St: FusedStream,
{
fn is_terminated(&self) -> bool {
self.remaining == 0 || self.stream.is_terminated()
}
}
// Forwarding impl of Sink from the underlying stream
#[cfg(feature = "sink")]
impl<S, Item> Sink<Item> for Take<S>
where S: Stream + Sink<Item>,
{
type Error = S::Error;
delegate_sink!(stream, Item);
}