Question

I need little help with inheritance in C++. I have code with same structure like this:

class IBase {
public:
    virtual long Dimensions() = 0;
};

class IShape : public IBase {
    virtual long Area() = 0;
};

class Rectangle : public IShape  {
private:
    long x;
public:
    long Dimensions() {return x};
    long Area() {return x*x};
};

class Rhombus: public IShape  {
private:
    long x;
    long fi;
public:
    long Dimensions() {return x};
    long Area() {return x*x*sin(fi)};
};

As you can see, implementation of Dimensions() is same for both classes. Now I wan’t to do something like this:

class BaseImplementation : public IBase {
protected:
    long x;
public:
    virtual long Dimensions() {return x};
};

class Rectangle : public IShape, public BaseImplementation {
public:
    long Area() {return x*x};
};

class Rhombus: public IShape, public BaseImplementation {
private:
    long fi;
public:
    long Area() {return x*x*sin(fi)};
};

Is possible to insert implementation of method Dimensions() into class Rhombus from BaseImplementation? Is this supported in some version of C++ standard?
Thx.

Answer 1

The problem with your hierarchy is that your Rectangle now inherits IBase twice: once through IShape, and once through BaseImplementation. C++ feature called Virtual Inheritance is designed to deal with situations like that. Note that you need to make IShape‘s inheriting IBase virtual public as well.