1 // { dg-do compile { target c++17 } } 2 // { dg-options "-fconcepts" } 3 4 template<typename T> C()5 concept bool C() { return __is_class(T); } 6 7 template<C T> struct S; 8 9 struct X { }; 10 11 // Not a valid explicit specialization, int does not satisfy C. 12 template<> struct S<int> { }; // { dg-error "constraint" } 13 14 int main() { } 15