Thanks for the answer, that's exactly what I wanted to know. On Jul 23, 1:59 pm, Rich Hickey <richhic...@gmail.com> wrote: > On Wed, Jul 22, 2009 at 4:33 PM, Dragan Djuric<draga...@gmail.com> wrote: > > > I've just read in the Stuart's book that multimethod dispatching on > > something other than Java inheritance is rarely used. It seems to me > > that there is a huge potential for their use in something that I do, > > so I'd add "yet" to his words. Anyway, what I would ask someone from > > the core team, or someone else that knows the internals is: > > How fast the multimethods dispatch performs with large taxonomies > > compared to Java inheritance or small taxonomies? For example, a 1000 > > or thousands elements in different taxonomies (or even a million?). Is > > it designed to perform well in such cases? > > Multimethod dispatch cost is the dispatch function + a single hashmap > lookup. If there is no match, there is a single one-time matching > process, the results of which are cached per multimethod. > Ancestor/descendant relationships are precalculated on modification of > the hierarchy, so isa? (for keywords) is a map lookup, not a tree > walk. All caches are invalidated on any modification to the hierarchy. > > There is currently no per-call-site caching, nor any optimization for > specialized cases (e.g. single dispatch). So, it is not going to be as > fast as Java inheritance. OTOH, the model is simple - what you see is > what you get, and scalability of the hashmaps from 1000s to millions > is also good, and again something you can directly try out. > > Rich
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