Re: How to prevent a function in base class being overloaded from child class

From: Jeff Schwab (jeffrey.schwab_at_rcn.com)
Date: 03/21/05 

Date: Mon, 21 Mar 2005 17:06:37 -0500

modemer wrote:
> Suppose I am a base class designer,
> I believe my func() in base class is the best solution for certain goal.

You are entitled to your opinion.

> This base class is going to be used by other programmers, they are just
> allowed to create their own child class inherated from my base class, but I
> don't want to write any email notice to say "func() is reserved for base
> class, don't use it in your derived class,

Can you make func() private?

> otherwise base::func() will never
> be called when child::func() is called", I want to know how to let compiler
> raise an error when the programmer happened defines func() in his child
> class.

Why do you care about an unrelated function in a derived class?

If you want to limit access to the internals of your Base objects, make
those internals private, and provide access only through methods in the
base class. E.g:

#include <iostream>

struct Base {
public:
        Base( ): m_i( 0 ) { }
        virtual ~Base( ) { }

        virtual void set( int i ) {
                // Override me all you want. You can't set m_i
                // without going through proper channels.

                std::cout << "I am the One True Way to set m_i.\n";
                m_i = i;
        }

        virtual int get( ) {
                std::cout << "I am the One True Way to get m_i.\n";
                return m_i;
        }
        
                
private:

        Base( Base const& ) {
                throw "Don't copy Base.\n";
        }

        Base operator = ( Base const& ) {
                throw "Don't assign to Base.\n";
        }

        int m_i;
};

struct Derived: Base {
        void set( int i ) {
                // For a compile time error, try this: m_i = i;

                Base::set( i ); // Pretty much your only option.
        }
};

int main( ) {
        Derived d;
        d.set( 3 );
}

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