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
use std::{borrow::Borrow, ops::Deref};
pub trait Shareable<'a> {
#[doc(hidden)]
type Shared: Copy + Borrow<Self> + 'a;
#[doc(hidden)]
fn share(&'a self) -> Self::Shared;
}
pub struct Share<'a, T: ?Sized + Shareable<'a>> {
shared: T::Shared,
}
impl<'a, T> Share<'a, T>
where
T: ?Sized + Shareable<'a>,
{
pub fn new(reference: &'a T) -> Self {
Share {
shared: reference.share(),
}
}
}
impl<'a, T> Deref for Share<'a, T>
where
T: ?Sized + Shareable<'a>,
{
type Target = T;
fn deref(&self) -> &T {
self.shared.borrow()
}
}
impl<'a, T> Shareable<'a> for &'a T
where
T: 'a,
{
type Shared = &'a T;
fn share(&'a self) -> &'a T {
*self
}
}
#[macro_export]
macro_rules! shareable {
($t:ty) => {
impl<'a> Shareable<'a> for $t {
type Shared = &'a $t;
fn share(&'a self) -> &'a $t {
self
}
}
};
($t:ty: Copy) => {
impl<'a> Shareable<'a> for $t {
type Shared = $t;
fn share(&self) -> $t {
*self
}
}
};
}
#[test]
fn copy() {
#[derive(Copy, Clone)]
struct Foo;
shareable!(Foo: Copy);
let _: Foo = Share::new(&Foo).shared;
}
#[test]
fn reference() {
#[derive(Clone)]
struct Foo;
shareable!(Foo);
let _: &Foo = Share::new(&Foo).shared;
}