1 use super::assert_stream;
2 use crate::stream::{select_with_strategy, PollNext, SelectWithStrategy};
3 use core::pin::Pin;
4 use futures_core::stream::{FusedStream, Stream};
5 use futures_core::task::{Context, Poll};
6 use pin_project_lite::pin_project;
7
8 pin_project! {
9 /// Stream for the [`select()`] function.
10 #[derive(Debug)]
11 #[must_use = "streams do nothing unless polled"]
12 pub struct Select<St1, St2> {
13 #[pin]
14 inner: SelectWithStrategy<St1, St2, fn(&mut PollNext)-> PollNext, PollNext>,
15 }
16 }
17
18 /// This function will attempt to pull items from both streams. Each
19 /// stream will be polled in a round-robin fashion, and whenever a stream is
20 /// ready to yield an item that item is yielded.
21 ///
22 /// After one of the two input streams completes, the remaining one will be
23 /// polled exclusively. The returned stream completes when both input
24 /// streams have completed.
25 ///
26 /// Note that this function consumes both streams and returns a wrapped
27 /// version of them.
28 ///
29 /// ## Examples
30 ///
31 /// ```rust
32 /// # futures::executor::block_on(async {
33 /// use futures::stream::{ repeat, select, StreamExt };
34 ///
35 /// let left = repeat(1);
36 /// let right = repeat(2);
37 ///
38 /// let mut out = select(left, right);
39 ///
40 /// for _ in 0..100 {
41 /// // We should be alternating.
42 /// assert_eq!(1, out.select_next_some().await);
43 /// assert_eq!(2, out.select_next_some().await);
44 /// }
45 /// # });
46 /// ```
select<St1, St2>(stream1: St1, stream2: St2) -> Select<St1, St2> where St1: Stream, St2: Stream<Item = St1::Item>,47 pub fn select<St1, St2>(stream1: St1, stream2: St2) -> Select<St1, St2>
48 where
49 St1: Stream,
50 St2: Stream<Item = St1::Item>,
51 {
52 fn round_robin(last: &mut PollNext) -> PollNext {
53 last.toggle()
54 }
55
56 assert_stream::<St1::Item, _>(Select {
57 inner: select_with_strategy(stream1, stream2, round_robin),
58 })
59 }
60
61 impl<St1, St2> Select<St1, St2> {
62 /// Acquires a reference to the underlying streams that this combinator is
63 /// pulling from.
get_ref(&self) -> (&St1, &St2)64 pub fn get_ref(&self) -> (&St1, &St2) {
65 self.inner.get_ref()
66 }
67
68 /// Acquires a mutable reference to the underlying streams that this
69 /// combinator is pulling from.
70 ///
71 /// Note that care must be taken to avoid tampering with the state of the
72 /// stream which may otherwise confuse this combinator.
get_mut(&mut self) -> (&mut St1, &mut St2)73 pub fn get_mut(&mut self) -> (&mut St1, &mut St2) {
74 self.inner.get_mut()
75 }
76
77 /// Acquires a pinned mutable reference to the underlying streams that this
78 /// combinator is pulling from.
79 ///
80 /// Note that care must be taken to avoid tampering with the state of the
81 /// stream which may otherwise confuse this combinator.
get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut St1>, Pin<&mut St2>)82 pub fn get_pin_mut(self: Pin<&mut Self>) -> (Pin<&mut St1>, Pin<&mut St2>) {
83 let this = self.project();
84 this.inner.get_pin_mut()
85 }
86
87 /// Consumes this combinator, returning the underlying streams.
88 ///
89 /// Note that this may discard intermediate state of this combinator, so
90 /// care should be taken to avoid losing resources when this is called.
into_inner(self) -> (St1, St2)91 pub fn into_inner(self) -> (St1, St2) {
92 self.inner.into_inner()
93 }
94 }
95
96 impl<St1, St2> FusedStream for Select<St1, St2>
97 where
98 St1: Stream,
99 St2: Stream<Item = St1::Item>,
100 {
is_terminated(&self) -> bool101 fn is_terminated(&self) -> bool {
102 self.inner.is_terminated()
103 }
104 }
105
106 impl<St1, St2> Stream for Select<St1, St2>
107 where
108 St1: Stream,
109 St2: Stream<Item = St1::Item>,
110 {
111 type Item = St1::Item;
112
poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>>113 fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> {
114 let this = self.project();
115 this.inner.poll_next(cx)
116 }
117 }
118