A map that creates a random handle on insertion to use when retrieving.

The raison d'être for this map is:

• You want to put something in a map, but you have no key. Means you do not want to use a HashMap or BTreeMap .

• You want to forget the details of what you put in to later retrieve it with a simple handle, and you are not interested in how many equal objects you insert. Means you do not want to use a HashSet or HashMultiSet .

• You want a persistent handle to refer to the item you put in the map. Means you do not want to use a Vec.

The implementation uses a HashMap that does not actually hash. The contained HashMap can be borrowed (.as_hash_map()), so all HashMap functions that do not change the map are at your disposal.