1 | use core::pin::Pin; |
2 | use futures_core::future::{FusedFuture, Future}; |
3 | use futures_core::ready; |
4 | use futures_core::task::{Context, Poll}; |
5 | use pin_project_lite::pin_project; |
6 | |
7 | use crate::fns::FnOnce1; |
8 | |
9 | pin_project! { |
10 | /// Internal Map future |
11 | #[project = MapProj] |
12 | #[project_replace = MapProjReplace] |
13 | #[derive(Debug)] |
14 | #[must_use = "futures do nothing unless you `.await` or poll them" ] |
15 | pub enum Map<Fut, F> { |
16 | Incomplete { |
17 | #[pin] |
18 | future: Fut, |
19 | f: F, |
20 | }, |
21 | Complete, |
22 | } |
23 | } |
24 | |
25 | impl<Fut, F> Map<Fut, F> { |
26 | /// Creates a new Map. |
27 | pub(crate) fn new(future: Fut, f: F) -> Self { |
28 | Self::Incomplete { future, f } |
29 | } |
30 | } |
31 | |
32 | impl<Fut, F, T> FusedFuture for Map<Fut, F> |
33 | where |
34 | Fut: Future, |
35 | F: FnOnce1<Fut::Output, Output = T>, |
36 | { |
37 | fn is_terminated(&self) -> bool { |
38 | match self { |
39 | Self::Incomplete { .. } => false, |
40 | Self::Complete => true, |
41 | } |
42 | } |
43 | } |
44 | |
45 | impl<Fut, F, T> Future for Map<Fut, F> |
46 | where |
47 | Fut: Future, |
48 | F: FnOnce1<Fut::Output, Output = T>, |
49 | { |
50 | type Output = T; |
51 | |
52 | fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> { |
53 | match self.as_mut().project() { |
54 | MapProj::Incomplete { future, .. } => { |
55 | let output = ready!(future.poll(cx)); |
56 | match self.project_replace(Map::Complete) { |
57 | MapProjReplace::Incomplete { f, .. } => Poll::Ready(f.call_once(output)), |
58 | MapProjReplace::Complete => unreachable!(), |
59 | } |
60 | } |
61 | MapProj::Complete => { |
62 | panic!("Map must not be polled after it returned `Poll::Ready`" ) |
63 | } |
64 | } |
65 | } |
66 | } |
67 | |