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
use core::pin::Pin;
use core::ptr;
use futures_core::future::{FusedFuture, Future};
use futures_core::task::{Context, Poll};
use pin_project::{pin_project, project};
use crate::fns::FnOnce1;
#[pin_project]
#[derive(Debug)]
#[must_use = "futures do nothing unless you `.await` or poll them"]
pub enum Map<Fut, F> {
Incomplete {
#[pin]
future: Fut,
f: F,
},
Complete,
}
struct UnsafeMarkAsComplete<Fut, F>(*mut Map<Fut, F>);
impl<Fut, F> Drop for UnsafeMarkAsComplete<Fut, F> {
fn drop(&mut self) {
unsafe {
ptr::write(self.0, Map::Complete);
}
}
}
impl<Fut, F> Map<Fut, F> {
pub(crate) fn new(future: Fut, f: F) -> Map<Fut, F> {
Map::Incomplete { future, f }
}
}
impl<Fut, F, T> FusedFuture for Map<Fut, F>
where Fut: Future,
F: FnOnce1<Fut::Output, Output=T>,
{
fn is_terminated(&self) -> bool {
match self {
Map::Incomplete { .. } => false,
Map::Complete => true,
}
}
}
impl<Fut, F, T> Future for Map<Fut, F>
where Fut: Future,
F: FnOnce1<Fut::Output, Output=T>,
{
type Output = T;
#[project]
fn poll(mut self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<T> {
unsafe {
let self_ptr: *mut Self = self.as_mut().get_unchecked_mut();
match &mut *self_ptr {
Map::Incomplete { future, f } => {
let mut future = Pin::new_unchecked(future);
let output = match future.as_mut().poll(cx) {
Poll::Ready(x) => x,
Poll::Pending => return Poll::Pending,
};
let f = ptr::read(f);
{
let _cleanup = UnsafeMarkAsComplete(self_ptr);
ptr::drop_in_place(future.get_unchecked_mut());
};
Poll::Ready(f.call_once(output))
},
Map::Complete => panic!("Map must not be polled after it returned `Poll::Ready`"),
}
}
}
}