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
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172

#![allow(non_snake_case)]

use core::fmt;
use core::mem;

use {Future, Poll, IntoFuture, Async};

macro_rules! generate {
    ($(
        $(#[$doc:meta])*
        ($Join:ident, $new:ident, <A, $($B:ident),*>),
    )*) => ($(
        $(#[$doc])*
        #[must_use = "futures do nothing unless polled"]
        pub struct $Join<A, $($B),*>
            where A: Future,
                  $($B: Future<Error=A::Error>),*
        {
            a: MaybeDone<A>,
            $($B: MaybeDone<$B>,)*
        }

        impl<A, $($B),*> fmt::Debug for $Join<A, $($B),*>
            where A: Future + fmt::Debug,
                  A::Item: fmt::Debug,
                  $(
                      $B: Future<Error=A::Error> + fmt::Debug,
                      $B::Item: fmt::Debug
                  ),*
        {
            fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
                fmt.debug_struct(stringify!($Join))
                    .field("a", &self.a)
                    $(.field(stringify!($B), &self.$B))*
                    .finish()
            }
        }

        pub fn $new<A, $($B),*>(a: A, $($B: $B),*) -> $Join<A, $($B),*>
            where A: Future,
                  $($B: Future<Error=A::Error>),*
        {
            $Join {
                a: MaybeDone::NotYet(a),
                $($B: MaybeDone::NotYet($B)),*
            }
        }

        impl<A, $($B),*> $Join<A, $($B),*>
            where A: Future,
                  $($B: Future<Error=A::Error>),*
        {
            fn erase(&mut self) {
                self.a = MaybeDone::Gone;
                $(self.$B = MaybeDone::Gone;)*
            }
        }

        impl<A, $($B),*> Future for $Join<A, $($B),*>
            where A: Future,
                  $($B: Future<Error=A::Error>),*
        {
            type Item = (A::Item, $($B::Item),*);
            type Error = A::Error;

            fn poll(&mut self) -> Poll<Self::Item, Self::Error> {
                let mut all_done = match self.a.poll() {
                    Ok(done) => done,
                    Err(e) => {
                        self.erase();
                        return Err(e)
                    }
                };
                $(
                    all_done = match self.$B.poll() {
                        Ok(done) => all_done && done,
                        Err(e) => {
                            self.erase();
                            return Err(e)
                        }
                    };
                )*

                if all_done {
                    Ok(Async::Ready((self.a.take(), $(self.$B.take()),*)))
                } else {
                    Ok(Async::NotReady)
                }
            }
        }

        impl<A, $($B),*> IntoFuture for (A, $($B),*)
            where A: IntoFuture,
        $(
            $B: IntoFuture<Error=A::Error>
        ),*
        {
            type Future = $Join<A::Future, $($B::Future),*>;
            type Item = (A::Item, $($B::Item),*);
            type Error = A::Error;

            fn into_future(self) -> Self::Future {
                match self {
                    (a, $($B),+) => {
                        $new(
                            IntoFuture::into_future(a),
                            $(IntoFuture::into_future($B)),+
                        )
                    }
                }
            }
        }

    )*)
}

generate! {
    /// Future for the `join` combinator, waiting for two futures to
    /// complete.
    ///
    /// This is created by the `Future::join` method.
    (Join, new, <A, B>),

    /// Future for the `join3` combinator, waiting for three futures to
    /// complete.
    ///
    /// This is created by the `Future::join3` method.
    (Join3, new3, <A, B, C>),

    /// Future for the `join4` combinator, waiting for four futures to
    /// complete.
    ///
    /// This is created by the `Future::join4` method.
    (Join4, new4, <A, B, C, D>),

    /// Future for the `join5` combinator, waiting for five futures to
    /// complete.
    ///
    /// This is created by the `Future::join5` method.
    (Join5, new5, <A, B, C, D, E>),
}

#[derive(Debug)]
enum MaybeDone<A: Future> {
    NotYet(A),
    Done(A::Item),
    Gone,
}

impl<A: Future> MaybeDone<A> {
    fn poll(&mut self) -> Result<bool, A::Error> {
        let res = match *self {
            MaybeDone::NotYet(ref mut a) => a.poll()?,
            MaybeDone::Done(_) => return Ok(true),
            MaybeDone::Gone => panic!("cannot poll Join twice"),
        };
        match res {
            Async::Ready(res) => {
                *self = MaybeDone::Done(res);
                Ok(true)
            }
            Async::NotReady => Ok(false),
        }
    }

    fn take(&mut self) -> A::Item {
        match mem::replace(self, MaybeDone::Gone) {
            MaybeDone::Done(a) => a,
            _ => panic!(),
        }
    }
}