::equals

#include <type_traits>
#include <utility>

namespace equals_details {

    template<typename... Args>
    constexpr bool equals(Args&&...);

    template<typename T, typename U>
    constexpr bool equals(T&& lhs, U&& rhs) noexcept(noexcept(std::forward<T>(lhs) == std::forward<U>(rhs))) {
        return std::forward<T>(lhs) == std::forward<U>(rhs);
    }

    template<typename T, typename U, typename... Args>
    constexpr bool equals(T&& lhs, U&& rhs, Args&&... args)

        noexcept(noexcept(std::forward<T>(lhs) == std::forward<U>(rhs)) &&
                 noexcept(equals(std::forward<U>(rhs), std::forward<Args>(args)...))) {

        return std::forward<T>(lhs) == std::forward<U>(rhs) &&
            equals(std::forward<T>(lhs), std::forward<Args>(args)...);

    }

}

// some information:
// doesn't participate in overload resolution if (sizeof...(Args) < 2)
// return: (a1 == a2 && a2 == a3 && ... && a(n - 1) == a(n)), where n = sizeof...(Args)
// exceptions: noexcept(false) if any comparasion yields noexcept(false)

template<typename... Args>
constexpr auto equals(Args&&... args) -> std::enable_if_t<sizeof...(Args) >= 2, bool> {

    return equals_details::equals(std::forward<Args>(args)...);

}