Re: Virtual Constructors
On Feb 27, 3:39 pm, dave_mikes...@fastmail.fm wrote:
On Feb 27, 10:35 am, "Carl R. Davies" <nwsg...@googlemail.com> wrote:
"As we have seen (section 14.2) C++ supports virtual destructors. Like
many other object oriented languages (e.g., Java), however, the notion
of a virtual constructor is not supported. The absence of a virtual
constructor turns into a problem when only a base class reference or
pointer is available, and a copy of a derived class object is
required."
What's wrong with down casting the base class pointer and using
assignment?
Bad design. If you design your class hierarchy correctly, client code
should be unaware of derived classes and work only through base class
pointers.
Ok, is it because the client code might not know what the derived
class is at time of writing so it's unable to down cast?
1. Framework code declares classes Base and Derived " class Derived :
public Base "
2. So in the client code:
Derived *ptr = new Derived();
Then calls a function that only knows Base:
void func( Base *inPtr )
{
// Can't down cast because doesn't know existence of Derived
// So how does Clone() help here?
}
Apologies for being persistent, I would like to know so I can
recognise the need for "Prototype Pattern" in the future.
Thanks.