src/librustc_error_codes/error_codes/E0261.md

   1 When using a lifetime like `'a` in a type, it must be declared before being
   2 used.
   3
   4 These two examples illustrate the problem:
   5
   6 ```compile_fail,E0261
   7 // error, use of undeclared lifetime name `'a`
   8 fn foo(x: &'a str) { }
   9
  10 struct Foo {
  11     // error, use of undeclared lifetime name `'a`
  12     x: &'a str,
  13 }
  14 ```
  15
  16 These can be fixed by declaring lifetime parameters:
  17
  18 ```
  19 struct Foo<'a> {
  20     x: &'a str,
  21 }
  22
  23 fn foo<'a>(x: &'a str) {}
  24 ```
  25
  26 Impl blocks declare lifetime parameters separately. You need to add lifetime
  27 parameters to an impl block if you're implementing a type that has a lifetime
  28 parameter of its own.
  29 For example:
  30
  31 ```compile_fail,E0261
  32 struct Foo<'a> {
  33     x: &'a str,
  34 }
  35
  36 // error,  use of undeclared lifetime name `'a`
  37 impl Foo<'a> {
  38     fn foo<'a>(x: &'a str) {}
  39 }
  40 ```
  41
  42 This is fixed by declaring the impl block like this:
  43
  44 ```
  45 struct Foo<'a> {
  46     x: &'a str,
  47 }
  48
  49 // correct
  50 impl<'a> Foo<'a> {
  51     fn foo(x: &'a str) {}
  52 }
  53 ```