Template classes and containers

[Prakash Bande]

Hi,

I have a template class as below:
template <class _T> class myclass{
public:
myclass(){ obj = new _T();}
_T* obj;
_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

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<somecla ss>
f1(a);
}
void f1(base *a)
{
// I want to do this here.
a->callmethod() ; // Would have worked if -> could return
myclass<somecla ss>*
}

Any suggestions?

Thanks,
Prakash

[Alf P. Steinbach]

Re: Template classes and containers

* Prakash Bande:[color=blue]
>
> I have a template class as below:
> template <class _T> class myclass{[/color]

Underscore followed by uppercase letter is reserved for the
implementation.
[color=blue]
> public:
> myclass(){ obj = new _T();}
> _T* obj;[/color]

This data member should not be public.
[color=blue]
> _T* operator->() (return obj;}
> };[/color]

[color=blue]
>
> 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[/color]

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


[color=blue]
> 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<somecla ss>
> f1(a);
> }
> void f1(base *a)
> {
> // I want to do this here.
> a->callmethod() ; // Would have worked if -> could return
> myclass<somecla ss>*
> }[/color]

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.
Q: What is the most annoying thing on usenet and in e-mail?