compiler/rustc_error_codes/src/error_codes/E0600.md

   1 An unary operator was used on a type which doesn't implement it.
   2
   3 Erroneous code example:
   4
   5 ```compile_fail,E0600
   6 enum Question {
   7     Yes,
   8     No,
   9 }
  10
  11 !Question::Yes; // error: cannot apply unary operator `!` to type `Question`
  12 ```
  13
  14 In this case, `Question` would need to implement the `std::ops::Not` trait in
  15 order to be able to use `!` on it. Let's implement it:
  16
  17 ```
  18 use std::ops::Not;
  19
  20 enum Question {
  21     Yes,
  22     No,
  23 }
  24
  25 // We implement the `Not` trait on the enum.
  26 impl Not for Question {
  27     type Output = bool;
  28
  29     fn not(self) -> bool {
  30         match self {
  31             Question::Yes => false, // If the `Answer` is `Yes`, then it
  32                                     // returns false.
  33             Question::No => true, // And here we do the opposite.
  34         }
  35     }
  36 }
  37
  38 assert_eq!(!Question::Yes, false);
  39 assert_eq!(!Question::No, true);
  40 ```