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
|
// Test that we correctly infer variance for region parameters in
// various self-contained types.
#![feature(rustc_attrs)]
// Regions that just appear in normal spots are contravariant:
#[rustc_variance]
struct Test2<'a, 'b, 'c> { //~ ERROR ['a: +, 'b: +, 'c: +]
x: &'a isize,
y: &'b [isize],
c: &'c str
}
// Those same annotations in function arguments become covariant:
#[rustc_variance]
struct Test3<'a, 'b, 'c> { //~ ERROR ['a: -, 'b: -, 'c: -]
x: extern "Rust" fn(&'a isize),
y: extern "Rust" fn(&'b [isize]),
c: extern "Rust" fn(&'c str),
}
// Mutability induces invariance:
#[rustc_variance]
struct Test4<'a, 'b:'a> { //~ ERROR ['a: +, 'b: o]
x: &'a mut &'b isize,
}
// Mutability induces invariance, even when in a
// contravariant context:
#[rustc_variance]
struct Test5<'a, 'b:'a> { //~ ERROR ['a: -, 'b: o]
x: extern "Rust" fn(&'a mut &'b isize),
}
// Invariance is a trap from which NO ONE CAN ESCAPE.
// In other words, even though the `&'b isize` occurs in
// an argument list (which is contravariant), that
// argument list occurs in an invariant context.
#[rustc_variance]
struct Test6<'a, 'b:'a> { //~ ERROR ['a: +, 'b: o]
x: &'a mut extern "Rust" fn(&'b isize),
}
// No uses at all is bivariant:
#[rustc_variance]
struct Test7<'a> { //~ ERROR ['a: *]
//~^ ERROR: `'a` is never used
x: isize
}
// Try enums too.
#[rustc_variance]
enum Test8<'a, 'b, 'c:'b> { //~ ERROR ['a: -, 'b: +, 'c: o]
Test8A(extern "Rust" fn(&'a isize)),
Test8B(&'b [isize]),
Test8C(&'b mut &'c str),
}
fn main() {}
|
