Tristan, SequenceableCollection abstracts using integers to index a collection; from there, subclasses (OrderedCollection is one of them) specialize the behavior to create growable and non-growable collections, collections specific to certain types of objects, etc. The Squeak/Pharo hierarchy browsers are **terrible** which greatly complicates building an understanding of such things. If you use or have access to Windows, you might grab the Community Edition of Dolphin Smalltalk if only to use their class hierarchy browser to look around the collections hierarchy. Dolphin has the best IDE in the business. Another question you might be asking is which collection class to use? The workhorses include Dictionary, Bag, SortedCollection, OrderedCollection, and sometimes Array; String and ByteArray count too, though they and things like FloatArray hold only specific types of objects for speed, gc efficiency, external calls, etc.. For reasons completely inscrutable to me after more than 15 years of Smalltalk use, streams like to work with and grow an Array far more than an OrderedCollection. Some things are best tolerate than understood :) Does that help? Bill ________________________________________ From: pharo-project-bounces@lists.gforge.inria.fr [pharo-project-bounces@lists.gforge.inria.fr] On Behalf Of Tristan Bourgois [tr.bourgois@laposte.net] Sent: Wednesday, May 26, 2010 10:19 AM To: pharo-project@lists.gforge.inria.fr Subject: [Pharo-project] difference between Sequenceable and Ordered Does anybody can explain the difference between a Sequenceable Collection and an Ordered Collection? Thanks. Tristan Bourgois. -- View this message in context: http://forum.world.st/difference-between-Sequenceable-and-Ordered-tp2231718p... Sent from the Pharo Smalltalk mailing list archive at Nabble.com. _______________________________________________ Pharo-project mailing list Pharo-project@lists.gforge.inria.fr http://lists.gforge.inria.fr/cgi-bin/mailman/listinfo/pharo-project