src/test/ui/rfc-2632-const-trait-impl/specialization/const-default-const-specialized.rs

   1 // Tests that a const default trait impl can be specialized by another const
   2 // trait impl and that the specializing impl will be used during const-eval.
   3
   4 // run-pass
   5
   6 #![feature(const_trait_impl)]
   7 #![feature(min_specialization)]
   8
   9 #[const_trait]
  10 trait Value {
  11     fn value() -> u32;
  12 }
  13
  14 const fn get_value<T: ~const Value>() -> u32 {
  15     T::value()
  16 }
  17
  18 impl<T> const Value for T {
  19     default fn value() -> u32 {
  20         0
  21     }
  22 }
  23
  24 struct FortyTwo;
  25
  26 impl const Value for FortyTwo {
  27     fn value() -> u32 {
  28         42
  29     }
  30 }
  31
  32 const ZERO: u32 = get_value::<()>();
  33
  34 const FORTY_TWO: u32 = get_value::<FortyTwo>();
  35
  36 fn main() {
  37     assert_eq!(ZERO, 0);
  38     assert_eq!(FORTY_TWO, 42);
  39 }