src/librustc_error_codes/error_codes/E0411.md

   1 The `Self` keyword was used outside an impl, trait, or type definition.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0411
   6 <Self>::foo; // error: use of `Self` outside of an impl, trait, or type
   7              // definition
   8 ```
   9
  10 The `Self` keyword represents the current type, which explains why it can only
  11 be used inside an impl, trait, or type definition. It gives access to the
  12 associated items of a type:
  13
  14 ```
  15 trait Foo {
  16     type Bar;
  17 }
  18
  19 trait Baz : Foo {
  20     fn bar() -> Self::Bar; // like this
  21 }
  22 ```
  23
  24 However, be careful when two types have a common associated type:
  25
  26 ```compile_fail
  27 trait Foo {
  28     type Bar;
  29 }
  30
  31 trait Foo2 {
  32     type Bar;
  33 }
  34
  35 trait Baz : Foo + Foo2 {
  36     fn bar() -> Self::Bar;
  37     // error: ambiguous associated type `Bar` in bounds of `Self`
  38 }
  39 ```
  40
  41 This problem can be solved by specifying from which trait we want to use the
  42 `Bar` type:
  43
  44 ```
  45 trait Foo {
  46     type Bar;
  47 }
  48
  49 trait Foo2 {
  50     type Bar;
  51 }
  52
  53 trait Baz : Foo + Foo2 {
  54     fn bar() -> <Self as Foo>::Bar; // ok!
  55 }
  56 ```