Dynamic Constructors in C++???

[sohail_k]

Can anyone explain me what are Dynamic Constructors in C++?
If possible give some example or provide with some reference article/link

Thanks in advance

[Graham]

I've not heard the term Dynamic Constructor used, but I'll take a guess that it's equivalent to the so-called "virtual constructor" or "clone method".

Basically, it's a way of constructing an object based on the run-time type of some existing object. It basically uses standard virtual functions/polymorphism.

class base
{
public:
    virtual base* create() = 0;
    virtual base* clone() = 0;

protected:
    base();
    base(const base&);
};

virtual der1 : public base
{
public:
    base* create() { return new der1; }
    base* clone() { return new der1(*this); }
    // etc...
};

virtual der2 : public base
{
public:
    base* create() { return new der2; }
    base* clone() { return new der2(*this); }
    // etc...
};

int main()
{
    base* b = new der1;

    base* b1 = b->create();
    base* b2 = b->clone();
}

In the above, if I change the initialisation of b so that it points to a der2, then b1 and b2 will also point to a der2 object (a brand new one in the case of b1, and a copy of *b in the case of b2).

[sohail_k]

Hi Graham,
Thanks for the reply.
Even I hadn't heard about this so called "Dynamic Constructors"
But I was asked this question in an Interview. (Or did they actually meant Dynamic construction and it was mispelled as Constructor )
Thanks a lot

Regards,
Sohail