// build-pass #![allow(incomplete_features)] #![feature(generic_const_exprs)] use std::marker::PhantomData; fn main() { let x = FooImpl::<BarImpl<1>> { phantom: PhantomData }; let _ = x.foo::<BarImpl<1>>(); } trait Foo<T> where T: Bar, { fn foo<U>(&self) where T: Operation<U>, <T as Operation<U>>::Output: Bar; } struct FooImpl<T> where T: Bar, { phantom: PhantomData<T>, } impl<T> Foo<T> for FooImpl<T> where T: Bar, { fn foo<U>(&self) where T: Operation<U>, <T as Operation<U>>::Output: Bar, { <<T as Operation<U>>::Output as Bar>::error_occurs_here(); } } trait Bar { fn error_occurs_here(); } struct BarImpl<const N: usize>; impl<const N: usize> Bar for BarImpl<N> { fn error_occurs_here() {} } trait Operation<Rhs> { type Output; } //// Part-A: This causes error. impl<const M: usize, const N: usize> Operation<BarImpl<M>> for BarImpl<N> where BarImpl<{ N + M }>: Sized, { type Output = BarImpl<{ N + M }>; } //// Part-B: This doesn't cause error. // impl<const M: usize, const N: usize> Operation<BarImpl<M>> for BarImpl<N> { // type Output = BarImpl<M>; // } //// Part-C: This also doesn't cause error. // impl<const M: usize, const N: usize> Operation<BarImpl<M>> for BarImpl<N> { // type Output = BarImpl<{ M }>; // }