src/test/ui/const-generics/invariant.rs

   1 #![feature(generic_const_exprs)]
   2 #![allow(incomplete_features)]
   3 use std::marker::PhantomData;
   4
   5 trait SadBee {
   6     const ASSOC: usize;
   7 }
   8 // fn(&'static ())` is a supertype of `for<'a> fn(&'a ())` while
   9 // we allow two different impls for these types, leading
  10 // to different const eval results.
  11 impl SadBee for for<'a> fn(&'a ()) {
  12     const ASSOC: usize = 0;
  13 }
  14 impl SadBee for fn(&'static ()) {
  15     //~^ WARNING conflicting implementations of trait
  16     //~| WARNING this was previously accepted
  17     const ASSOC: usize = 100;
  18 }
  19
  20 struct Foo<T: SadBee>([u8; <T as SadBee>::ASSOC], PhantomData<T>)
  21 where
  22     [(); <T as SadBee>::ASSOC]: ;
  23
  24 fn covariant(
  25     v: &'static Foo<for<'a> fn(&'a ())>
  26 ) -> &'static Foo<fn(&'static ())> {
  27     v //~ ERROR mismatched types
  28 }
  29
  30 fn main() {
  31     let y = covariant(&Foo([], PhantomData));
  32     println!("{:?}", y.0);
  33 }