Traits

Of course traits can also be generic. Here we define one which reimplements
the Drop trait as a generic method to drop itself and an input.

  1. // Non-copyable types.
  2. struct Empty;
  3. struct Null;
  5. // A trait generic over `T`.
  6. trait DoubleDrop<T> {
  7.     // Define a method on the caller type which takes an
  8.     // additional single parameter `T` and does nothing with it.
  9.     fn double_drop(self, _: T);
  10. }
  12. // Implement `DoubleDrop<T>` for any generic parameter `T` and
  13. // caller `U`.
  14. impl<T, U> DoubleDrop<T> for U {
  15.     // This method takes ownership of both passed arguments,
  16.     // deallocating both.
  17.     fn double_drop(self, _: T) {}
  18. }
  20. fn main() {
  21.     let empty = Empty;
  22.     let null  = Null;
  24.     // Deallocate `empty` and `null`.
  25.     empty.double_drop(null);
  27.     //empty;
  28.     //null;
  29.     // ^ TODO: Try uncommenting these lines.
  30. }

See also:

Drop, struct, and trait