class Interface
{
public:
    virtual void foo(int) = 0;
};

class PreviousClass : public Interface
{
public:
    void foo(int)
    {
        /* implementation */
    }
};

template <typename T>
class CommonImpl
{
public:
    void foo(T) { /* implementation */ }
}

class ConcreteClassInt : public Interface, public CommonImpl
{
public:
    ConcreteClass(): CommonImpl<int>() {}
}