Re: Restricting access should be illegal?

walter@digitalmars-nospamm.com (Walter Bright) wrote (abridged):


What would be gained by making it an error?


The closest I have seen is where the derived class needs to provide the
base class interface, but discourages its use in favour of a new interface
of its own.

    class Version_1 {
    public:
        virtual void slowFunc();
    };
    
    class Version_2 : public Version_1 {
    public:
        virtual void fastFunc(); // Like slowFunc() but faster.
    private:
        virtual void slowFunc(); // Now depreciated.
    };

Here Version_1 is an old, obsolete interface, and Version_2 is the new
improved one. All objects that support Version_2 also support Version_1,
and there is an implicit conversion to make passing the new objects to old
routines convenient. However, new routines are strongly encouraged to use
the new interface.

    void newRoutine( Version_2 &object ) {
        // object.slowFunc(); // Error.
        Version_1 &old = object;
        old.slowFunc(); // OK but depreciated.
        object.fastFunc(); // Preferred.
    }

So far as I know this hasn't been written up as a design pattern, and I
don't know if you'd consider it legitimate if it was. The question is
whether we would be better off if it were forbidden at the language level.

-- Dave Harris, Nottingham, UK.

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