Polymorphically Persisting Custom Collections
The versions of
saveGuts() and
restoreGuts() that the Essential Tools Module built into class
RWCollection are sufficient for most collection classes. The function
RWCollection::saveGuts() works by repeatedly calling:
RWvostream& operator<<(RWvostream&, const RWCollectable&);
for each item in the collection. Similarly, RWCollection::restoreGuts() works by repeatedly calling:
RWvistream& operator>>(RWvistream&, RWCollectable*&);
This operator allocates a new object of the proper type off the heap, then calls
insert(). Because all of the Rogue Wave Smalltalk-like collection classes inherit from
RWCollection, they all use this mechanism.
If you decide to write your own collection classes that inherit from class
RWCollection, you will rarely have to define your own
saveGuts() or
restoreGuts().
There are exceptions. For example, class
RWBinaryTree has its own version of
saveGuts(). This is necessary because the default version of
saveGuts() stores items in order. For a binary tree, this would result in a severely unbalanced tree when the tree was read back in—essentially, the degenerate case of a linked list. Hence,
RWBinaryTree’s version of
saveGuts() stores the tree level-by-level.
When you design your class, you must determine whether it has similar special requirements which may need a custom version of saveGuts() and restoreGuts().
