CODEWITHSUNDEEP
c++pointersinheritance
j76goatboy
j76goatboy

Reputation: 445

C++ Inheriting Function Pointer that can be used with derived only methods

This is a simplified example of a design problem.

I have the class Base. It has a function pointer type and a protected variable of that function pointer type. 

#ifndef BASE_H
#define BASE_H

class Base {

    typedef void (Base::*FunctionPointer) ( void );

protected:

    FunctionPointer pointer;

};

#endif  /* BASE_H */

Then I have the class Derived that inherits from Base. This class wants to be able to set the inherited pointer variable equal to addresses for it's own methods, not ones inherited or overridden from Base.

#ifndef DERIVED_H
#define DERIVED_H

#include "Base.h"

class Derived : public Base{

public:
    Derived()
    {
        pointer = &Derived::ProtectedMethod;
    }

    void ProtectedMethod()
    {

    }

};

#endif  /* DERIVED_H */

The problem is that the type of function pointers (void (Base::*FunctionPointer) ( void ) and void (Derived::*FunctionPointer) ( void )) are different.

In Short

Is there a way to have a pointer variable in a base class that can be assigned to derived classes methods (not overridden)?

Upvotes: 1

Views: 48

Answers (2)

skypjack
skypjack

Reputation: 50540

I'm with @RSahu: it is not possible for they are unrelated types.
I'm adding this answer for the sake of curiosity.

You can do something similar with the CRTP idiom:

template<class D>
struct B {
    using FnType = void(D::*)();
    FnType ptr{nullptr};
};

struct D: B<D> {
    D(): B{} {
        ptr = &D::method;
    }

    void method() { }
};

This is not exactly what you asked for, but it is a viable solution at least.

Upvotes: 1

R Sahu
R Sahu

Reputation: 206567

Is there a way to have a pointer variable in a base class that can be assigned to derived classes methods (not overridden)?

No, you cannot do that. They are unrelated types.

Upvotes: 4

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