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// { dg-do compile { target c++20 } }
// { dg-additional-options "-fconcepts" }
#include <type_traits>
inline constexpr bool and_impl() { return true; }
template <class OperandFirst, class... OperandsRest>
constexpr bool and_impl(OperandFirst operand_first,
OperandsRest... operands_rest) {
return operand_first && and_impl(operands_rest...);
}
template <class... Operands> constexpr bool and_(Operands... operands) {
return and_impl(operands...);
}
template <class X> concept C = true;
// v1
template<int, class... Xs>
requires (and_(C<Xs>...))
constexpr int f(const Xs&... xs) {
return 0;
}
// v2
template<int, class... Xs>
constexpr int f(const Xs&... xs) {
return 1;
}
int main() {
static_assert(f<10>(3.0, 2.0f) == 0);
return 0;
}
// 2nd example
template <typename T, typename... Us>
concept AreType =
(std::is_same<T,Us>::value && ...);
// return true; gives the same overloaded error
// Function with constraint
template<typename T, AreType<T>... Us>
constexpr bool isValid(Us... us) {
return true;
}
// Function with no constraint
template<typename T, typename... U>
constexpr bool isValid(U... u) {
return false;
}
int main2() {
static_assert(isValid<int>(1)); // also isValid<int>(1, 2, 3); etc
return 0;
}
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