On Friday, April 20, 2012 4:01:54 PM UTC+9:30, David Jagoe wrote: > > > On 20 April 2012 07:08, Matthew Phillips <mattp...@gmail.com> wrote: > >> I've always liked the way assoc and dissoc return the original map >> instance when there's no change to be made. But this is not apparently >> true of records. e.g.: > > > Out of curiosity, why is this useful to you? > > I would imagine that the fact that it works like that for maps at the > moment is an implementation detail that you shouldn't rely upon. > > dissoc[iate]. Returns a new map of the same (hashed/sorted) type, > that does not contain a mapping for key(s). >
It's mainly that, when mentally reasoning about the performance of assoc and dissoc, I've been quite happy to say "this dissoc here will hardly ever actually need to *do* anything, thus have very little overhead GC-wise". This didn't turn out to be true of records, which was surprising. I haven't been impacted performance-wise, but it does seem like a missed optimisation opportunity: I'd be interested to hear if it's harder to do than I think in the record case. You're right that relying on identical? in code logic is a bad idea. Matthew. -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
