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 | /// ``` |
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, which: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. |
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. |
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. |
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. |
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 | { |
101 | 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 | |
113 | fn poll_next(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<St1::Item>> { |
114 | let this: Projection<'_, St1, St2> = self.project(); |
115 | this.inner.poll_next(cx) |
116 | } |
117 | } |
118 | |