Check if a class has a specific attribute

has_member.cpp

/** Defines structures that check if opts_t has an attribute called member.
 * 
 * has_member<opts_t> is a true type if the struct opts_t has an attribute called member.
 * has_member_v<opts_t> is true if the struct opts_t has a member called member.
 * 
 * @param member Attribute to be checked
 * 
 * @see https://stackoverflow.com/questions/1005476/how-to-detect-whether-there-is-a-specific-member-variable-in-class
 */
#define MEMBER_CHECKER(member) \
    template< class opts_t, typename = int > \
    struct has_ ## member : std::false_type { }; \
    \
    template< class opts_t > \
    struct has_ ## member< opts_t, \
        enable_if_t< \
            !is_same_v< \
                decltype(std::declval<opts_t>().member), \
                void > \
        , int > \
    > : std::true_type { }; \
    \
    template< class opts_t > \
    constexpr bool has_ ## member ## _v = has_ ## member<opts_t>::value;

// Activate checkers:
MEMBER_CHECKER(nb)
MEMBER_CHECKER(workPtr)