Logical Operator Type Traits

logical-operator-type-traits.cpp

#include <type_traits>

// impl ----------

#if (__cplusplus > 201402L)

using std::bool_constant;
using std::negation;
using std::conjunction;
using std::disjunction;

#else

template <bool B>
using bool_constant = std::integral_constant<bool, B>;

template <class T>
using negation = bool_constant<!T::value>;

template <class...>
struct conjunction {};

template <class T, class... Args>
struct conjunction<T, Args...> : bool_constant<T::value and conjunction<Args...>::value> {};

template <>
struct conjunction<> : std::true_type {};

template <class...>
struct disjunction {};

template <class T, class... Args>
struct disjunction<T, Args...> : bool_constant<T::value or disjunction<Args...>::value> {};

template <>
struct disjunction<> : std::false_type {};

#endif

// usage ----------

template <typename T, typename... Ts>
using is_same_all = conjunction<std::is_same<T, Ts>...>;

template <typename T, typename... Ts>
using is_same_either = disjunction<std::is_same<T, Ts>...>;

int main()
{
    static_assert(!is_same_all<int, int, int, int, int>::value, "all int");
    static_assert( is_same_all<int, int, int, int, float>::value, "not all int");
    static_assert(!is_same_either<int, bool, char, int, float>::value, "has int");
    return 0;
}

Logical Operator Type Traits (revision 1)