On Fri, Oct 30, 2009 at 9:31 PM, Josh Daghlian <daghl...@gmail.com> wrote:
> During the Boston Lisp Users meeting last November (?) I asked Rich > about whether seq's on mutable java.util.Collections were really > immutable if the underlying object (the Collection) was mutable. He > emphatically said that no, the seq is still immutable, and that it > caches values as it sees them. I just checked, and for ArrayList it > still works like Rich said: > > user> x > #<ArrayList [foo, bar, baz, quux] > > > user> (def y (seq x)) > #'user/ > y > user> (first y) > "foo" > user> (.add x 0 "zzz") > nil > user> x > #<ArrayList [zzz, foo, bar, baz, quux] > > > user> (first y) > "foo" > user> > > I am surprised that the same doesn't happen with java arrays. Sounds > like a bug, or at least a change request I'd second. > Interesting. I thought maybe inserting at the start might not affect the seq even if the maybe-bug did affect ArrayList, because it might just stay aligned with the existing elements. But no: user=> (def x (ArrayList. ["foo" "bar" "baz" "quux"])) #'user/x user=> x #<ArrayList [foo, bar, baz, quux]> user=> (def y (seq x)) #'user/y user=> (first y) "foo" user=> (.set x 0 "boo") "foo" user=> (first y) "foo" user=> (first x) "boo" So, (first y) doesn't morph even if you mutate the first cell of the ArrayList in place. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
