How Can C 11 Type Traits Detect the Presence of a Member Function with a Specific Signature?

Detecting Member Function Presence Using C 11 Type Traits

Question:

How can we determine if a class possesses a member function with a specific signature without requiring the class to provide it?

Elaboration of the Dilemma:

The problem arises when we need to perform custom operations based on the presence or absence of a particular member function in a class. Unlike cases where the class must provide the function, we seek a method to discern its existence for conditional processing. The ideal solution avoids global function overwriting, excessive stack invocations, and intrusive namespace declarations.

Template-Based Solution:

Utilizing C 11 type traits, we can devise a template function that verifies the existence of the target function:

template<typename C, typename Ret, typename... Args>
struct has_serialize {
    // Assertion to prevent instantiation with non-function arguments
    static_assert(
        std::integral_constant<T, false>::value,
        "Second template parameter needs to be of function type."
    );

    // Specialization to perform the check
    private:
        template<typename T>
        static constexpr auto check(T*)
        -> typename
            std::is_same<
                decltype( std::declval<T>().serialize( std::declval<Args>()... ) ),
                Ret    // ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
            >::type;  // attempt to call it and see if the return type is correct

        template<typename>
        static constexpr std::false_type check(...);

        typedef decltype(check<C>(0)) type;

    public:
        static constexpr bool value = type::value;
};

Usage:

We can now employ the has_serialize template to verify function existence within a class:

struct X {
    int serialize(const std::string&) { return 42; } 
};

struct Y : X {};

std::cout << has_serialize<X, int(const std::string&amp;)>::value; // prints 1

In the example above, has_serialize::value will also evaluate to true because inheritance preserves the function signature. This feature is a key advantage over the solution presented in the original thread.

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