如何检查派生类的可调用成员函数是否存在？

#include <type_traits>

// 检测成员函数 foo
template <typename T>
class has_foo {
    typedef char one;
    typedef struct { char a[2]; } two;

    template <typename C> static one test(decltype(&C::foo));
    template <typename C> static two test(...);

public:
    enum { value = sizeof(test<T>(0)) == sizeof(one) };
};

// 示例派生类
class Base {};
class Derived : public Base {
public:
    void foo() {}
};

int main() {
    bool hasFoo = has_foo<Derived>::value; // true
    return 0;
}

#include <type_traits>

class Base {};
class Derived : public Base {
public:
    void foo() {}
};

int main() {
    bool isFooMemberFunction = std::is_member_function_pointer<decltype(&Derived::foo)>::value; // true
    return 0;
}

#include <type_traits>

template <typename T>
typename std::enable_if<std::is_member_function_pointer<decltype(&T::foo)>::value, void>::type
call_foo(T& obj) {
    obj.foo();
}

class Base {};
class Derived : public Base {
public:
    void foo() {}
};

int main() {
    Derived d;
    call_foo(d); // 正常调用
    return 0;
}