mbr@bellcore.com (Mark Rosenstein) writes:

>Reading through "Standard C++ Update" in the July/August issue of C++
>report, it wasn't clear whether it would be possible to use the
>run-time type identification extension to dynamically allocate objects
>of dynamically determined type.
[reformatted for brevity:]
>class employee { ...  };
>class programmer : public employee{ ...  };
>
>is there a way to do:
>
employee *pe;
>employee *fred = new typeid(*pe);
>
>[obviously this is not a reasonable syntax, but what I want is fred to
>a new programmer.]

There couldn't be a way of doing this directly, because not all employees
can be created from scratch using the default constructor - you may
need to pass some parameters to the constructor, and these parameters
may be different for each different derived class.

You can achieve the desired effect by using a virtual function make()
such as
 employee* employee::make() { return new employee; }
 employee* programmer::make() { return new employee; }
 fred = pe->make();

(If employee is an abstract base class then employee::make() should be
pure virtual).

--
Fergus Henderson                     fjh@munta.cs.mu.OZ.AU

Reading through "Standard C++ Update" in the July/August issue of C++
report, it wasn't clear whether it would be possible to use the
run-time type identification extension to dynamically allocate objects
of dynamically determined type.