Passing a class to a pure virtual function (without templates)

From:
"captaincurk@googlemail.com" <captaincurk@googlemail.com>
Newsgroups:
comp.lang.c++
Date:
Wed, 22 Apr 2009 02:13:45 -0700 (PDT)
Message-ID:
<c2f1beb6-064b-40d3-a0e9-8572bb0c4a5a@c36g2000yqn.googlegroups.com>
Hello there,

I have the following problem:

// abstract base class
class A {
public:
  virtual void addItems() =0;
};

class B : public A {
public:
  virtual void addItems() {
    // here I need to instantiate objects of a given type
  }
}

In B's something() function, I need to fill an internal list with
objects of a specific type. I need some way to pass my classname to
the function. Naturally I would try

template <class InstantiationClass> virtual void addItems() {
  list.push_back(new InstantiationClass());
}

Unfortunately that does not work, because pure virtual template
functions obviously don't work. Now I could move the template up to
the class B, but that is not very useful, as in my main program I will
call addItems very often and with different classes as parameters. Is
there an easy way to do this?

One way I could think of is to make a global constructor for each
class I want to use and then pass a function reference, but that
creates a LOT of new functions, which are only called once. And also
since my code resides in a framework, the call to addItems should be
very easy and straightforward and work with custom classes.

Thanks in advance and cheers,
Jonas

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