How to Detect Inherited Member Functions Using SFINAE in C ?

Using SFINAE to Check for Inherited Member Functions

SFINAE (Substitution Failure Is Not An Error) is a powerful technique in C that allows for compile-time evaluation of expressions. It can be used to detect the presence of member functions, including inherited ones.

The following code demonstrates one approach to testing for inherited member functions:

<code class="cpp">#include <iostream>

template<typename Type>
class has_foo
{
    class yes { char m; };
    class no { yes m[2]; };
    struct BaseMixin
    {
        void foo() {}
    };
    struct Base : public Type, public BaseMixin {};
    template<typename T, T t> class Helper {};
    template<typename U>
    static no deduce(U*, Helper<void(BaseMixin::*)(), &U::foo>* = 0);
    static yes deduce(...);
public:
    static const bool result = sizeof(yes) == sizeof(deduce((Base*)(0)));
};

struct A
{
    void foo();
};

struct B : A {};

struct C {};

int main()
{
    using namespace std;
    cout << boolalpha << has_foo<A>::result << endl;
    cout << boolalpha << has_foo<B>::result << endl;
    cout << boolalpha << has_foo<C>::result;
}</code>

Output:

true
true
false

This approach utilizes class derivation and template metaprogramming to determine whether a given type inherits a method. The BaseMixin class defines the desired method, and the Base class serves as an intermediate type that's derived from both the target type and BaseMixin. This allows for the use of SFINAE to deduce whether the method exists on the target type.

The has_foo class then uses this deduction to provide a compile-time constant indicating whether the method is present. This allows for efficient and extensible code that can dynamically adjust its behavior based on the presence or absence of inherited member functions.

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