Metafunctions for checking for existence of member and free functions

has_free_function.hpp

template < typename T >
class has_FUNCTION_NAME_function {
    template < typename U = T >
    static ::std::true_type test(decltype(FUNCTION_NAME(::std::declval<T>()), void())*);
    static ::std::false_type test(...);
public:
    using type = decltype(test(nullptr));
    static constexpr bool value = type::value;
};

has_member.hpp

template< typename T >
class has_MEMBER_NAME_member {
    template < typename U = T>
    static ::std::true_type test( decltype( &U::MEMBER_NAME )* );
    static ::std::false_type test(...);
public:
    using type = decltype(test(nullptr));
    static constexpr bool value = type::value;
};

has_template_member.hpp

template < typename T, typename ... Args >
class has_MEMBER_NAME_member {
    template < typename U = T>
    static ::std::true_type
    test( decltype(::std::declval<U>().MEMBER_NAME(::std::declval<Args>()...), void())* );

    static ::std::false_type test(...);
public:
    using type = decltype(test(nullptr));
    static constexpr bool value = type::value;
};