Question

I have a class A, which is an external class and not under my control, but i can design the specs of it.

In my code, I want to attach statically some properties and methods to A. I could inherit from A and attach the new functionality. But, since i don’t know the exact specs of A, I cannot provide the constructors of A in my derived class internalA.

I could use the decorator pattern, but it seems a bit overkill since i want to decorate at build time.

Any suggestion to solve it nicely ?

Answer 1

I believe a reference to the externalA should be sufficient.

template <typename A>
class InternalA {
    A &externalA;
    int property1;
    std::string property2;
    //...
public:
    InternalA (A &extA, int prop1, std::string prop2 /*...*/);
    // accessors to properties and to externalA...
};

But, I may have misunderstood your question.