With inheritance items (methods, attributes) can be redefined. The old item is hidden by the new one. But redefined items can be accessed by a qualified notation:

xx.yy

here xx denotes the name of the parent class which previously defines the item and yy denotes the item.

Now we would like to consider the following scenario:

Assume, class A contains a method B. The implementation of method B contains a method call to method C. Now class A_derived is derived from A. A_derived inherits the methods B and C from A, but it redefines method C. If method B is invoked for an object of class A_derived, the question is which version of method C is invoked by B. The inherited but hidden version or the redefined version?

To ensure proper functionality of inherited method B Objective VHDL will automatically call the inherited version of C!

To allow method B to invoke the redefined version of method B, method B must be called with the prefix this. The following example illustrates the application of this.