Look at Digitalk's VSE 3.1 and above. It does exactly what you asked for.
-----Original Message----- From: Stephen Pair [mailto:spair@advantive.com] Sent: Friday, March 31, 2000 8:09 AM To: squeak@cs.uiuc.edu Subject: RE: Musings on Identity
On a related note, how about splitting the collection hieararchy in two, an implementation hiearcy, and an interface hierarchy. Since the optimal implementation of a collection is often dependent on it's size. It would be nice to have a set of collection classes, whose instances morph their implementation (under specified criteria) into something more appropriate for the characteristics of the collection.
Maybe something like:
Dictionary SmallDictionary MediumDictionary LargeDictionary HugeDictionary MutableDictionary
Of course, then what do you do with the existing subclasses of Dictionary (split hieararchy problem).
Someone told me that IBM Smalltalk was like this early on, but dropped it for some reason.
- Stephen
-----Original Message----- From: Georg Gollmann [mailto:georg.gollmann@tuwien.ac.at] Sent: Friday, March 31, 2000 8:58 AM To: squeak@cs.uiuc.edu Subject: Musings on Identity
Some ideas for Squeak 3 :-)
Currently the object header contains a 12 bit field for an identity hash. This is too little and too much at the same time: it takes valuable space in the object header and it is insufficient for large IdentitySets or -Dictionaries.
Therefore how about ditching this field alltogether and reimplementing IdentitySets as arrays sorted by oop ?
Lookup should be reasonably fast using binary search. Since the garbage collector only shifts objects but does not shuffle them, the sort order would not be affected by compaction. Become operations would necessitate resorting of affected sets however. IdentityDictionaries could be built using parallel arrays for keys and values. Insertion and deletion might become slow for very large sets. If this really becomes an issue those sets could be split into a sorted array of subsets with a two stage lookup.
Has this been done before ? Any flaws in the resoning ?
Georg -- ---- Dipl.Ing. Georg Gollmann TU-Wien, Zentraler Informatikdienst Wiedner Hauptstr. 8-10 phon:(+43-1) 58801 - 42022 A-1040 Wien fax: (+43-1) 58801 - 42099 mail:gollmann@zid.tuwien.ac.at http://macos.tuwien.ac.at/Gollmann.html