compiler/rustc_error_codes/src/error_codes/E0623.md

   1 A lifetime didn't match what was expected.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0623
   6 struct Foo<'a> {
   7     x: &'a isize,
   8 }
   9
  10 fn bar<'short, 'long>(c: Foo<'short>, l: &'long isize) {
  11     let _: Foo<'long> = c; // error!
  12 }
  13 ```
  14
  15 In this example, we tried to set a value with an incompatible lifetime to
  16 another one (`'long` is unrelated to `'short`). We can solve this issue in
  17 two different ways:
  18
  19 Either we make `'short` live at least as long as `'long`:
  20
  21 ```
  22 struct Foo<'a> {
  23     x: &'a isize,
  24 }
  25
  26 // we set 'short to live at least as long as 'long
  27 fn bar<'short: 'long, 'long>(c: Foo<'short>, l: &'long isize) {
  28     let _: Foo<'long> = c; // ok!
  29 }
  30 ```
  31
  32 Or we use only one lifetime:
  33
  34 ```
  35 struct Foo<'a> {
  36     x: &'a isize,
  37 }
  38 fn bar<'short>(c: Foo<'short>, l: &'short isize) {
  39     let _: Foo<'short> = c; // ok!
  40 }
  41 ```