Question

If I have two classes A and B defined as:

class A {
    map<int, int> mMap;
    vector<int> mVec;

    void method() {
      // do something with mMap and mVec 
    }
}

class B {
    map<int, double> mMap; // just an example of a map with a different signature

    ...
}

It is possible somehow to use everything A has in B but with the new map defined in B and without rewriting method ?

This is a simplified example of what I am trying to do: refactoring a big class with a new map.

Answer 1

If you want to use

std::map<int, Y>

instead of

std::map<int, X>

with the same code, to replace class A with class B, then there probably exists a strong correlation between the types X and Y.

In this case, if you cannot use templates on class A, a possible workaround may be to define implicit type conversion operators for both Y and X to X and Y respectively.

class X {
    operator Y() {
        Y y;
        // Conversion logic
        return y;
    }
};

By doing so, you don’t need to change the code of method as the insertion or access operations on the map will automatically call the implicit type conversion operators.

Warning note: the abuse of implicit conversion operators weakens the type safety checkings of the compiler that you may expect in other parts of the code (e.g.: wrong Y parameter passed to f(X &x)).