RTTI & Polymorphism

when you use polymorphic, you must enable RTTI. RTTI is C++ feature to determine object type in run-time.

The criticism refers to a programming style that uses switch-blocks to determine to dynamic type of an object and call the relevant member functions:

if (typeid(myobj)==typeid(CWnd))
...do CWnd stuff
else if (typeid(myobj)==typeid(CDilaog))
...do CDialog stuff

This style is the anathema of OOP. It hardwires the object's type to the program's logic, whereas in real OOP you wouldn't care about the dynamic type of myobj. Instead, you would use a virtual member function and override it in the derived classes. This way you could use the same line of code:

myobj.func(); //or pmyobj->func()

Depending only on the static type of myobj. More importantly, this code will work correctly even if you add new derived class to the hierarchy, whereas in the if-else sequence, you always need to add a new case for every new derived class. The use of dynamic_type instead of typeid can solve some of these design problems but it introduces another problem: performance.