HP Integrity NonStop J-Series - Manual (Page 158)

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©Copyright 1996 Rogue Wave Software
Virtual Functions Inherited From RWCollection
The Smalltalk-like collection classes inherit from the abstract base class RWCollection , which in
turn inherits from the abstract base class RWCollectable , described in Chapters 13 ( Tables of the
Smalltalk-like Classes ) and 15 . (Thus do we produce collections of collections, but that is another
story.)
An abstract base class is a class intended to be inherited by some other class, not used as itself per
se. If you think of it as a kind of virtual class, you can easily project the meaning of virtual
functions. These virtual functions provide a blueprint of functionality for the derived class. As an
abstract base class,
RWCollection provides a blueprint for collection classes by declaring various
virtual functions, such as insert(), remove(), entries(), and so on.
This section describes the virtual functions inherited by the Smalltalk-like collections. Any of
these collections can be expected to understand them.
insert()
You can put a pointer to an object into a collection by using the virtual function insert():
virtual RWCollectable* insert(RWCollectable*);
This function inserts in the way most natural for the collection. Faced with a stack, it pushes an
item onto the stack. Faced with a queue, it appends the item to the queue. In a sorted collection, it
inserts the new item so that items before it compare less than itself, items after it compare greater
than itself, and items equal compare equal, if duplicates are allowed. See the example in
Chapter
13 ( Example of Tables of Smalltalk-like Classes ) for an example using insert().
You must always insert pointers to real objects. Since all RWCollection classes need to
dereference their contents for some methods such as find(), inserting a zero will cause such
methods to crash. If you must store an empty object, we suggest you create and insert a default
constructed object of the appropriate type, such as
RWCollectable *. If you know you won't be
deleting every object in the RWCollection, you could also choose the global RWnilCollectable,
which is a pointer to a cached RWCollectable object. But beware! Since there is only one
RWnilCollectable, if you delete it, any other reference to it will be referencing invalid memory.