Question

I am not sure how to ask this, but hopefully someone will understand. Lets say I have 3 different classes. Class A, Class B and Class C. Class C should take either Class A or Class B as a parameter in the constructor and store it in a private variable.

This is easy with overloaded constructors. My question is how can Class C automagically use the correct class depending on what constructor was used? (Note these 2 classes are similar, but come from different libraries and thus no shared base class). Is this possible with templates? I do not have a lot of experience with templates.

Answer 1

You can do it quite easy with templates:

class A;
class B;

template<class AorB>
class C
{
public:
    C(AorB aorb)
        : aorb_(aorb)
        { }

private:
    AorB aorb_;
};

What this does is that inside the class C the identifier AorB can be used as any other class, in fact it doesn’t even have to be an instance of A or B but can be any class.

Can be used like this:

A myA;
B myB;

C<A> myCWithA(myA);
C<B> myCWithB(myB);

---

There is however one thing you have to remember when creating classes using templates: The specification and implementation can no longer be split into separate header and source files. All of the code have to be available in the header file.

The syntax of the member functions are also a little different.

Example:

template<class T>
class C
{
public:
    ...

    void someFunction();
};

template<class T>
C<T>::someFunction()
{
    ...
}