Mixin in c++

mixin.cc

#include <iostream>

using namespace std;

class A {
public:
        void a() { cout << "a" << endl; }
};

template<typename T> struct Mixin: T {
public:
        void twice() {
                this->a();
                this->a();
        }
};

void mixin() {
        Mixin<A> ma;
        ma.twice();
}

int main() {
        mixin();
}