Re: Interface design question

Paavo Helde <>
Thu, 11 Oct 2012 16:57:47 -0500
<XnsA0EA9CC5B9C0myfirstnameosapriee@> wrote in


      Have a design related question and hope to hear some insights.

      Interfaces using abstract classes impose restriction(s) on it's
      derived implementations.
        - The most widely used restriction is to IMPLEMENT Function(s)

The functions are made abstract when it does not make sense to provide
some common functionality for all derived classes..

        Is it permissible to have similar kind of restriction for any
        data members in the interface? In a way that if some one wants
        to implement the interface it also must initialize certain

Data members in the base class are used when it does make sense to
provide some common functionality for all derived classes. In this sense
this is the exact opposite of abstract functions.

        Say for a TCP/IP it absolutely necessary to have peer's IP
        address and Port number. So, is wise to impose a restriction
        to pass above variable to initialize the class.

        class IP4Connection
                    explicit IP4Connection( string ip, uint port);
                    virtual int send() = 0;
                    virtual int listen() = 0;
                    virtual int reconnect() = 0;
                    std::string ip;
                    uint port;

In principle all data should be private. Having protected data members
already looses encapsulation and is a bit of design smell. If the data is
only used by derived classes, it should reside in the derived classes

Just my 1 cent

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