On Mon, May 12, 2014 at 12:53 PM, Alex Miller <a...@puredanger.com> wrote:
> My recommendation in Java would be the same - using mutable objects as > keys in a map (where mutability changes the hashcode) is a bug waiting to > happen. > Although I used java.util.ArrayList in the sample REPL session showing the surprising behavior, I never said anything about the Java types used in our application being mutable. That gets at my point: the "best" Java collection values, the only ones that make good hashmap keys, are immutable, but Clojure still gives them this mixed status where they're equiv but not hasheq to IPersistentCollections w/ the same contents. [Having made that point again, I'll now admit that under the cover of java.util.List<V>, the lists in messages our app receives are ArrayLists :-), BUT they're never mutated, and we'd have the same issue if they were Guava ImmutableList<V>, which is a fine value type (so long as V is immutable).] In general, Clojure treats Java collections (and arrays) as values now ... > but if you do mutation, then any Clojure guarantees are off (in hashing, in > STM, etc). I think that's been generally a happy compromise so far. The > question is to what extent that should continue. > I'm totally happy to see crazy things happen to anyone who treats a mutable collection as a value and then mutates it. It may even be that this could be supported without much of a hit. Strings, > numbers, keywords, symbols, and all Clojure collections should be handled > above the suggested change and that covers most common key types. Some > research would need to be done on what common non-Clojure classes (hence > not IHashEq implementors) fall into the final else case - java.lang.Class > is one that comes to mind which is used a lot inside Clojure itself. > I like the sound of this. One of your comments on the ticket mentioned JVM inlining issues, which scared me. Is it a safe bet that protocol dispatch would be too slow for hasheq? -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
