// CS0767: Cannot implement interface `I<T,U>' with the specified type parameters because it causes method `I<int,int>.Foo(ref int)' to differ on parameter modifiers only // Line: 10 interface I<T, U> { void Foo(ref U t); void Foo(out T u); } class A : I<int, int> { void I<int, int>.Foo(ref int arg) { } public virtual void Foo(out int arg) { arg = 8; } }