CODEWITHSUNDEEP
c++oop
Name
Name

Reputation: 118

Override class member variable

I'm running into an inheritance problem and I don't know if my solution is elegant. I have classes like this

class Var
{
public:
    virtual void doSomething();
}
class DerivedVar : public Var
{
public:
    virtual void doSomething();
    void doSomethingElse();
}

I also have MyDerived that inherits from MyBase. MyBase has a member of type Var while MyDerived needs to have a member of DerivedVar so it can call doSomething(). Currently, I'm using template to solve this problem

template<typename VarType>
class MyBase
{
protected:
    VarType var;
public:
    MyBase() { var.doSomething(); }
}

class MyDerived : public MyBase<DerivedVar>
{
public:
    MyDerived() : MyBase() { var.doSomethingElse(); }

}

I want to know if there's a better way to do this (eg. without the need of using template)

Upvotes: 3

Views: 204

Answers (1)

Cheers and hth. - Alf
Cheers and hth. - Alf

Reputation: 145269

If you want or need to avoid the templating then you need to allocate the covariant type data member dynamically.

A good approach is then to pass a factory up the constructor chain (it can be a defaulted constructor argument), and invoke it in the base class.

An ungood approach, but very popular in the early 1990s, is to use two-phase initialization.

OK, I anticipated issue that you have not yet run into.

But you will. ;-)

That said, if you can make the template approach work that's probably best.

Most direct solution, least amount of workarounds and code and design adaptions.

Upvotes: 1

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