Advanced Class Topics

Run-time type information

Every class in QDL has a run-time type information (RTTI) structure, encapsulated in part by an instance of the built-in ClassInfo class.

The information provided by this structure includes:

• The name of the class
• Links to base and derived classes
• Pointers to Virtual functions

Only the first two items are accessible through the ClassInfo structure. Every class with the Virtual and/or Template modifiers, or which contains Virtual functions, has a pointer to the RTTI structure stored in each instance of the class.

Because of RTTI, you can do the following at run-time, given a reference to an instance of a class with an RTTI pointer:

• Get the string name of the class, its base classes and (possibly) derived classes
• Determine whether this reference actually refers to a derived class

Each time a class is derived from a base class, a new RTTI structure is created for the base class as well as the derived class. This is done so