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
|
// run-pass
#![feature(trait_upcasting)]
trait Foo: PartialEq<i32> + std::fmt::Debug + Send + Sync {
fn a(&self) -> i32 {
10
}
fn z(&self) -> i32 {
11
}
fn y(&self) -> i32 {
12
}
}
trait Bar: Foo {
fn b(&self) -> i32 {
20
}
fn w(&self) -> i32 {
21
}
}
trait Baz: Bar {
fn c(&self) -> i32 {
30
}
}
impl Foo for i32 {
fn a(&self) -> i32 {
100
}
}
impl Bar for i32 {
fn b(&self) -> i32 {
200
}
}
impl Baz for i32 {
fn c(&self) -> i32 {
300
}
}
// Note: upcast lifetime means a shorter lifetime.
fn upcast_baz<'a: 'b, 'b, T>(v: Box<dyn Baz + 'a>, _l: &'b T) -> Box<dyn Baz + 'b> {
v
}
fn upcast_bar<'a: 'b, 'b, T>(v: Box<dyn Bar + 'a>, _l: &'b T) -> Box<dyn Bar + 'b> {
v
}
fn upcast_foo<'a: 'b, 'b, T>(v: Box<dyn Foo + 'a>, _l: &'b T) -> Box<dyn Foo + 'b> {
v
}
fn main() {
let v = Box::new(1);
let l = &(); // dummy lifetime (shorter than `baz`)
let baz: Box<dyn Baz> = v.clone();
let u = upcast_baz(baz, &l);
assert_eq!(*u, 1);
assert_eq!(u.a(), 100);
assert_eq!(u.b(), 200);
assert_eq!(u.c(), 300);
let baz: Box<dyn Baz> = v.clone();
let bar: Box<dyn Bar> = baz;
let u = upcast_bar(bar, &l);
assert_eq!(*u, 1);
assert_eq!(u.a(), 100);
assert_eq!(u.b(), 200);
let baz: Box<dyn Baz> = v.clone();
let foo: Box<dyn Foo> = baz;
let u = upcast_foo(foo, &l);
assert_eq!(*u, 1);
assert_eq!(u.a(), 100);
let baz: Box<dyn Baz> = v.clone();
let bar: Box<dyn Bar> = baz;
let foo: Box<dyn Foo> = bar;
let u = upcast_foo(foo, &l);
assert_eq!(*u, 1);
assert_eq!(u.a(), 100);
}
|
