src/librustc_error_codes/error_codes/E0665.md

   1 The `Default` trait was derived on an enum.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0665
   6 #[derive(Default)]
   7 enum Food {
   8     Sweet,
   9     Salty,
  10 }
  11 ```
  12
  13 The `Default` cannot be derived on an enum for the simple reason that the
  14 compiler doesn't know which value to pick by default whereas it can for a
  15 struct as long as all its fields implement the `Default` trait as well.
  16
  17 If you still want to implement `Default` on your enum, you'll have to do it "by
  18 hand":
  19
  20 ```
  21 enum Food {
  22     Sweet,
  23     Salty,
  24 }
  25
  26 impl Default for Food {
  27     fn default() -> Food {
  28         Food::Sweet
  29     }
  30 }
  31 ```