completion 0.2.1

Utilities for writing completion-based asynchronous code
Documentation 
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
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156

//! `FlatMap` and `Flatten`.

use core::pin::Pin;
use core::task::{Context, Poll};

use completion_core::CompletionStream;
use futures_core::{ready, Stream};
use pin_project_lite::pin_project;

use crate::CompletionStreamExt;

use super::Map;

pin_project! {
    /// Stream for [`CompletionStreamExt::flat_map`].
    #[derive(Debug, Clone)]
    pub struct FlatMap<S: CompletionStream, U, F>
    where
        F: FnMut(S::Item) -> U,
    {
        #[pin]
        inner: Flatten<Map<S, F>>,
    }
}

impl<S: CompletionStream, U: CompletionStream, F: FnMut(S::Item) -> U> FlatMap<S, U, F> {
    pub(crate) fn new(stream: S, f: F) -> Self {
        Self {
            inner: stream.map(f).flatten(),
        }
    }
}

impl<S, U, F> CompletionStream for FlatMap<S, U, F>
where
    S: CompletionStream,
    U: CompletionStream,
    F: FnMut(S::Item) -> U,
{
    type Item = U::Item;

    unsafe fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        self.project().inner.poll_next(cx)
    }
    unsafe fn poll_cancel(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
        self.project().inner.poll_cancel(cx)
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        self.inner.size_hint()
    }
}

impl<S, U, F> Stream for FlatMap<S, U, F>
where
    S: CompletionStream + Stream<Item = <S as CompletionStream>::Item>,
    U: CompletionStream + Stream<Item = <U as CompletionStream>::Item>,
    F: FnMut(<S as CompletionStream>::Item) -> U,
{
    type Item = <Self as CompletionStream>::Item;
    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        #[inline]
        fn assert_is_stream<T: Stream>() {}
        assert_is_stream::<Flatten<Map<S, F>>>();

        unsafe { CompletionStream::poll_next(self, cx) }
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        CompletionStream::size_hint(self)
    }
}

pin_project! {
    /// Stream for [`CompletionStreamExt::flatten`].
    #[derive(Debug, Clone)]
    pub struct Flatten<S: CompletionStream> {
        #[pin]
        stream: S,
        #[pin]
        current: Option<S::Item>,
    }
}

impl<S: CompletionStream> Flatten<S> {
    pub(crate) fn new(stream: S) -> Self {
        Self {
            stream,
            current: None,
        }
    }
}

impl<S, U> CompletionStream for Flatten<S>
where
    S: CompletionStream<Item = U>,
    U: CompletionStream,
{
    type Item = U::Item;

    unsafe fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        let mut this = self.project();

        Poll::Ready(loop {
            if let Some(current) = this.current.as_mut().as_pin_mut() {
                if let Some(item) = ready!(current.poll_next(cx)) {
                    break Some(item);
                }
                this.current.set(None);
            }

            this.current
                .set(Some(match ready!(this.stream.as_mut().poll_next(cx)) {
                    Some(stream) => stream,
                    None => break None,
                }));
        })
    }

    unsafe fn poll_cancel(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<()> {
        let mut this = self.project();

        if let Some(current) = this.current.as_mut().as_pin_mut() {
            current.poll_cancel(cx)
        } else {
            this.stream.poll_cancel(cx)
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let (_, stream_upper) = self.stream.size_hint();
        let (current_lower, current_upper) =
            self.current.as_ref().map_or((0, Some(0)), U::size_hint);
        (
            current_lower,
            if stream_upper == Some(0) {
                current_upper
            } else {
                None
            },
        )
    }
}

impl<S, U> Stream for Flatten<S>
where
    S: CompletionStream<Item = U> + Stream<Item = U>,
    U: CompletionStream + Stream<Item = <U as CompletionStream>::Item>,
{
    type Item = <Self as CompletionStream>::Item;

    fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Self::Item>> {
        unsafe { CompletionStream::poll_next(self, cx) }
    }
    fn size_hint(&self) -> (usize, Option<usize>) {
        CompletionStream::size_hint(self)
    }
}