Tools.h++ Manual

104011 Tandem Computers Incorporated 21-3
21
RWBag
RWBag
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RWCollection
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RWCollectable
Synopsis typedef RWBag Bag; // Smalltalk typedef.
#include <rw/rwbag.h>
RWBag h;
Description Class RWBag corresponds to the Smalltalk class Bag . It represents a group of
unordered elements, not accessible by an external key. Duplicates are allowed.
An object stored by RWBag must inherit abstract base class RWCollectable ,
with suitable definition for virtual functions hash() and isEqual() (see class
RWCollectable ). The function hash() is used to find objects with the same
hash value, then isEqual() is used to confirm the match.
Class RWBag is implemented by using an internal hashed dictionary
( RWHashDictionary ) which keeps track of the number of occurrences of an
item. If an item is added to the collection that compares equal ( isEqual ) to an
existing item in the collection, then the count is incremented.
Note – This means that only the first instance of a value is actually inserted:
subsequent instances cause the occurrence count to be incremented. This behavior
parallels the Smalltalk implementation of Bag .
Member function apply() and the iterator are called repeatedly according to
the count for an item.
See class RWHashTable if you want duplicates to be stored, rather than merely
counted.
Public constructors RWBag(size_t n = RWDEFAULT_CAPACITY);
Construct an empty bag with n buckets.
RWBag(const RWBag& b);
Copy constructor. A shallow copy of b will be made.