HP Integrity NonStop J-Series - Manual (Page 157)

you exceed the capacity of a vector-based collection class, it will automatically resize, but it
may exact a significant performance penalty to do so.
Note that the binary and B-tree classes can be considered sequenceable in the sense that they
are sorted, and therefore have an innate ordering. However, their ordering is determined
internally by the relative value of the collected objects, rather than by an insertion order. In
other words, you cannot arbitrarily insert an object into a sorted collection in any position you
want because it might not remain sorted. Hence, these classes are subclassed separately.
Dictionaries
Sometimes referred to as maps, dictionaries use an external key to find a value. The key and
value may be of different types, and in fact usually are. You can think of dictionaries as
associating a given key with a given value. For example, if you were building a symbol table in
a compiler, you might use the symbol name as the key, and its relocation address as the value.
This approach would contrast with your approach for a Set, where the name and address would
have to be encapsulated into one object.
Tools.h++ provides two dictionary classes: RWHashDictionary , implemented as a hash table,
and RWBTreeDictionary , implemented as a B-tree. For these classes, both keys and values
must inherit from the abstract base class RWCollectable .