HP Integrity NonStop J-Series - Manual (Page 281)

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©Copyright 1996 Rogue Wave Software
Multiple Inheritance
In Chapter 15 , we built a Bus class by inheriting from RWCollectable . If we had an existing Bus
class at hand, we might have saved ourselves some work by using multiple inheritance to create
a new class with the functionality of both Bus and RWCollectable as follows:
class CollectableBus : public RWCollectable, public Bus {
.
.
.
};
This is the approach taken by many of the Rogue Wave collectable classes; for example, class
RWCollectableString inherits from both class RWCollectable and class RWCString . The general
idea is to create your object first, then tack on the RWCollectable class to make the whole thing
collectable. This way, you will be able to use your objects for other things or in other situations,
where you might not want to inherit from class RWCollectable.
There is another good reason for using this approach: to avoid ambiguous base classes. Here's an
example:
class A { };
class B : public A { };
class C : public A { };
class D : public B, public C { };
void fun(A&);
main () {
D d;
fun(d); // Which A ?
}
There are two approaches to disambiguating the call to fun(). We can either change it to:
fun((B)d); // We mean B's occurrence of A