Re: Template classes and containers

From: Alf P. Steinbach (alfps_at_start.no)
Date: 09/02/04 

Date: Thu, 02 Sep 2004 05:15:48 GMT

* Prakash Bande:
>
> I have a template class as below:
> template <class _T> class myclass{

Underscore followed by uppercase letter is reserved for the
implementation.

> public:
> myclass(){ obj = new _T();}
> _T* obj;

This data member should not be public.

> _T* operator->() (return obj;}
> };

>
> I need to keep all the myclass objects in a STL container such as
> vector. But since every instantiation is a different type I cannot
> have a vector or myclass.
> So I derived myclass from a base class as below:
> class base{
> public:
> base(){}
> ~base(){}
> };
> template class<_T> myclass : public base

STL or standard library container requires among other things that your
objects can be safely copied -- can they?

 
> Now I have a vector of base objects.
> The problem is that I want to call -> operator. I cannot make it pure
> virtual in base since the return type depends on template resolution.
> I cannot typecast base pointer since I do not know type because of
> template. For example:
> f()
> {
> base *a = new myclass<someclass>
> f1(a);
> }
> void f1(base *a)
> {
> // I want to do this here.
> a->callmethod(); // Would have worked if -> could return
> myclass<someclass>*
> }

Try to explain why you "need" to have these objects in a single container,
or why you "need" to have them of different types. 

-- 
A: Because it messes up the order in which people normally read text.
Q: Why is it such a bad thing?
A: Top-posting.
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