1 #![feature(associated_type_defaults)]
2
3 // Associated type defaults may not be assumed inside the trait defining them.
4 // ie. they only resolve to `<Self as Tr>::A`, not the actual type `()`
5 trait Tr {
6 type A = (); //~ NOTE associated type defaults can't be assumed inside the trait defining them
7
f(p: Self::A)8 fn f(p: Self::A) {
9 let () = p;
10 //~^ ERROR mismatched types
11 //~| NOTE expected associated type, found `()`
12 //~| NOTE expected associated type `<Self as Tr>::A`
13 }
14 }
15
16 // An impl that doesn't override the type *can* assume the default.
17 impl Tr for () {
f(p: Self::A)18 fn f(p: Self::A) {
19 let () = p;
20 }
21 }
22
23 impl Tr for u8 {
24 type A = ();
25
f(p: Self::A)26 fn f(p: Self::A) {
27 let () = p;
28 }
29 }
30
31 trait AssocConst {
32 type Ty = u8; //~ NOTE associated type defaults can't be assumed inside the trait defining them
33
34 // Assoc. consts also cannot assume that default types hold
35 const C: Self::Ty = 0u8;
36 //~^ ERROR mismatched types
37 //~| NOTE expected associated type, found `u8`
38 //~| NOTE expected associated type `<Self as AssocConst>::Ty`
39 }
40
41 // An impl can, however
42 impl AssocConst for () {
43 const C: Self::Ty = 0u8;
44 }
45
main()46 fn main() {}
47