Re: list of all objects in a templated class

From:

Alan Woodland <ajw05@aber.ac.uk>

Newsgroups:

comp.lang.c++

Date:

Thu, 09 Jul 2009 14:03:30 +0100

Message-ID:

<q96hi6xtig.ln2@news.aber.ac.uk>

Ajay 0x007 wrote:

On Jul 9, 3:52 pm, Alan Woodland <aj...@aber.ac.uk> wrote:

Ajay 0x007 wrote:

Hi,
I have a templated class and I want to mantain a list pointers of all
objects of that class. How it can be achieved???
If i do like below (make list as static member variable of same class)
then the list will be different for all typename X, i.e.
template <typename X> class A{
    static std::vector<class<X>* > list;
    A(){
    list.push_back(this);
    }
};
If I make a global pointer instead of static member variable as above
then I need to provide actual argumenst to X which I cannot know in
advance.
Is their any way to achiev that?

How about another class that all A's inherit from? You could store
pointers to them without any trouble... you could even add one or more
virtual methods to that class to do something useful with!

What's your motivation for doing this though? There might be other
solutions too.

base class mantaining the list of templated class is not possible, How
the template argument be determined in base class??? i.e.

class base {
std::vector<class A<X>* > list;
};
class A:public base{
};
How the "X" in base class will be determined?

base won't know the X. You could store the type_info with each instance
in the list, but that smells of bad design.

In your application is X the infinite set of all user defined types? Or
is it some small restricted subset? There are things you could
potentially do if it's a small restricted subset here too.

I want to mantain a list of all pointers of a templated class which
will be extracted later on.

Why do you want to examine them though? What do you hope to achieve by
examining them? Why can't this be done through a pure virtual function
in base? Something seems odd with your design here, but we don't have
enough information to go with.

Alan