Hey Andy, It does matter with regard to visibility across threads - your example does not use a synchronization mechanism and there is no guarantee that other threads will ever see those changes (so don't ever ever do that :). But if you stick to the normal Clojure apis, all is good. I'd highly recommend reading JCIP to dive into the details.
Final field freeze is particularly weird and it baked my noodle when I first encountered it - here's a blog I wrote about it approx 697 years ago in internet time (and Brian Goetz backs me up in the comments :) http://tech.puredanger.com/2008/11/26/jmm-and-final-field-freeze/ Alex On Tuesday, May 6, 2014 7:35:43 PM UTC-5, Andy Fingerhut wrote: > > Alex, I may be unfamiliar with the definitions of truly immutable and > effectively immutable being used here, but if I can mutate the contents of > a Java Object array that is a final field after an object is constructed, > does it really matter that much if it is final? It is trivially easy to > mutate using Java access. Here is the example that I mentioned earlier in > this thread, copied here for convenience: > > user=> (def v [1 2 3]) > #'user/v > user=> (class v) > clojure.lang.PersistentVector > user=> v > [1 2 3] > user=> (aset (.tail v) 1 -2) > -2 > user=> v > [1 -2 3] > > Andy > > > On Tue, May 6, 2014 at 4:49 PM, Alex Miller <al...@puredanger.com<javascript:> > > wrote: > >> The Clojure persistent data structures are truly immutable - all fields >> are final and referred objects are not mutated after construction so that >> freeze occurs. One obvious exception are the transient variants ( >> http://clojure.org/transients). You can look at the code in >> https://github.com/clojure/clojure/tree/master/src/jvm/clojure/lang - >> any of the Persistent*.java. >> >> >> On Tuesday, May 6, 2014 4:11:49 PM UTC-5, Mike Fikes wrote: >>> >>> Are the persistent immutable data structures in Clojure "truly" >>> immutable (using final fields, relying on constructor freezing), or are >>> they mean to be merely effectively immutable (as defined in JICP)? >>> >> -- >> You received this message because you are subscribed to the Google >> Groups "Clojure" group. >> To post to this group, send email to clo...@googlegroups.com<javascript:> >> Note that posts from new members are moderated - please be patient with >> your first post. >> To unsubscribe from this group, send email to >> clojure+u...@googlegroups.com <javascript:> >> 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+u...@googlegroups.com <javascript:>. >> For more options, visit https://groups.google.com/d/optout. >> > > -- 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.
