src/test/ui/associated-consts/defaults-not-assumed-pass.rs

   1 // run-pass
   2
   3 trait Tr {
   4     const A: u8 = 255;
   5
   6     // This should not be a constant evaluation error (overflow). The value of
   7     // `Self::A` must not be assumed to hold inside the trait.
   8     const B: u8 = Self::A + 1;
   9 }
  10
  11 // An impl that doesn't override any constant will NOT cause a const eval error
  12 // just because it's defined, but only if the bad constant is used anywhere.
  13 // This matches the behavior without defaults.
  14 impl Tr for () {}
  15
  16 // An impl that overrides either constant with a suitable value will be fine.
  17 impl Tr for u8 {
  18     const A: u8 = 254;
  19 }
  20
  21 impl Tr for u16 {
  22     const B: u8 = 0;
  23 }
  24
  25 impl Tr for u32 {
  26     const A: u8 = 254;
  27     const B: u8 = 0;
  28 }
  29
  30 fn main() {
  31     assert_eq!(<() as Tr>::A, 255);
  32     //assert_eq!(<() as Tr>::B, 0);  // using this is an error
  33
  34     assert_eq!(<u8 as Tr>::A, 254);
  35     assert_eq!(<u8 as Tr>::B, 255);
  36
  37     assert_eq!(<u16 as Tr>::A, 255);
  38     assert_eq!(<u16 as Tr>::B, 0);
  39
  40     assert_eq!(<u32 as Tr>::A, 254);
  41     assert_eq!(<u32 as Tr>::B, 0);
  42 }