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// { dg-options "-std=c++17 -fconcepts" }
template<typename... Ts> struct are_same;
template<>
struct are_same<> {
static constexpr bool value = true;
};
template<typename T>
struct are_same<T> {
static constexpr bool value = true;
};
template<typename T, typename U, typename... Ts>
struct are_same<T, U, Ts...> {
static constexpr bool value =
__is_same_as(T, U) && are_same<U, Ts...>::value;
};
constexpr bool all_of() { return true; }
constexpr bool all_of(bool b) { return b; }
template<typename... Ts>
constexpr bool all_of(bool a, bool b, Ts... args) {
return (a && b) && all_of(b, args...);
}
template<typename... Ts>
concept bool C1 = are_same<Ts...>::value;
template<bool... Bs>
concept bool C2 = all_of(Bs...);
template<C1... Ts> struct S1 { }; // OK
S1<int, int, char> s1; // { dg-error "constraint failure|invalid type" }
template<C1 Ts> struct S2 { }; // { dg-error "variadic constraint" }
template<C2... Bs> struct S3 { }; // OK
S3<true, true, false> s3; // { dg-error "constraint failure|invalid type" }
template<C2 Bs> struct S4 { }; // { dg-error "variadic constraint" }
int main() { }
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