How can I create a polymorphic object on the stack?

Question

How do I allocate a polymorphic object on the stack? I\'m trying to do something similar to (trying to avoid heap allocation with new)?:

A* a = NULL;

switch         


        

Answer 1

Polymorphism doesn't work with values, you need a reference or a pointer. You can use a const reference to a temporary object polymorphically and it will have the lifetime of a stack object.

const A& = (use_b ? B() : A());

If you need to modify the object, you have no choice but to dynamically allocate it (unless you're using Microsoft's non-standard extension that lets you bind a temporary object to a non-const reference).