CODEWITHSUNDEEP
c++inheritanceclass-design
hansgans
hansgans

Reputation: 337

Class design: Class member inherits from the same base class

I'm thinking about a proper class design for the following case: Let's say I want to create a class design which resembles (mathematical) functions. All functions derive from base class Function. Now one could think of a function FuncB which is the sum of multiple objects of FuncA. In my case FuncB and FuncA are rather complicate objects but my current implementation boils down to:

class Function
{
    virtual double value() = 0;
};

class FuncA : public Function
{
public:
    virtual double value() {return v;}
private:
    double v;
};

class FuncB : public Function
{
    virtual double value() {
        double result = 0;
        for( auto i : v)
            result += i.value();
        return result;
    }
private:
    std::vector<DerivedA> v;
};

Somehow I would consider this as a bad class design since FuncB has a member which inherits from the same base class as the class itself. Any suggestions how to solve this more elegant?

Upvotes: 3

Views: 91

Answers (1)

mksteve
mksteve

Reputation: 13073

The composite design pattern 

class ContainerOfX : public X {
    typedef X* bestType;
    // maybe...
    // typedef std::shared_ptr<X> bestType;


    ...

    std::vector< bestType > subTypes;
};

It allows you to create a drawing system - where a composite object of different shapes can be treated as an agregate

obj->draw(); // draw house from various lines and boxes.

It allows you to create a simple script of things to do for do/undo logic.

Upvotes: 1

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