Re: Am I using NVI?

From:

Dragan Milenkovic <dragan@plusplus.rs>

Newsgroups:

comp.lang.c++.moderated

Date:

Thu, 18 Jun 2009 12:45:32 CST

Message-ID:

<h1dfqk$2mkr$1@adenine.netfront.net>

Martin T. wrote:

DeMarcus wrote:

In The C++ Programming Language 3rd ed. by Stroustrup, p.314 it explains
the use of pure virtual interfaces.

In C++ Coding Standards by Sutter & Alexandrescu it says:
Item 39: Consider making virtual functions nonpublic, and public
functions nonvirtual.

[snip]

Personally I have used it when it comes naturally (i.e. the Base class
need to do work before and after the virtual function anyway) and if I
just have an interface like the one you have above, I'll leave it at that.

Don't know if it helps or if I'm right, but I _always_ consider
delegation first. Of course, sometimes such design doesn't make sense...

My arguments are - separation of responsibilities, encapsulation...

class NVI_Base {
   public:
     void func() {
         setup();
         work();
         cleanup();
     }

   protected:
     virtual void work() = 0;
};

Becomes:

class NVI_Concrete {
   public:
     explicit NVI_Concrete(Worker * worker);

     void func() {
         setup()
         worker->work();
         cleanup();
     }
   private:
     Worker * worker;
};

class Worker {
  public:
     virtual void work() = 0;
};

Usually, Worker::work gets a state as an argument.

Maybe you could give a concrete example for analysis?

--
Dragan

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