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

use core::pin::Pin;
use futures_core::stream::{FusedStream, Stream};
use futures_core::task::{Context, Poll};
use futures_sink::Sink;
use pin_utils::{unsafe_pinned, unsafe_unpinned};

/// Stream for the [`skip`](super::StreamExt::skip) method.
#[derive(Debug)]
#[must_use = "streams do nothing unless polled"]
pub struct Skip<St> {
    stream: St,
    remaining: u64,
}

impl<St: Unpin> Unpin for Skip<St> {}

impl<St: Stream> Skip<St> {
    unsafe_pinned!(stream: St);
    unsafe_unpinned!(remaining: u64);

    pub(super) fn new(stream: St, n: u64) -> Skip<St> {
        Skip {
            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<'a>(self: Pin<&'a mut Self>) -> Pin<&'a 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: FusedStream> FusedStream for Skip<St> {
    fn is_terminated(&self) -> bool {
        self.stream.is_terminated()
    }
}

impl<St: Stream> Stream for Skip<St> {
    type Item = St::Item;

    fn poll_next(
        mut self: Pin<&mut Self>,
        cx: &mut Context<'_>,
    ) -> Poll<Option<St::Item>> {
        while self.remaining > 0 {
            match ready!(self.as_mut().stream().poll_next(cx)) {
                Some(_) => *self.as_mut().remaining() -= 1,
                None => return Poll::Ready(None),
            }
        }

        self.as_mut().stream().poll_next(cx)
    }
}

// Forwarding impl of Sink from the underlying stream
impl<S, Item> Sink<Item> for Skip<S>
where
    S: Stream + Sink<Item>,
{
    type SinkError = S::SinkError;

    delegate_sink!(stream, Item);
}