On Wednesday, October 22, 2014 4:51:23 PM UTC-4, Ambrose Bonnaire-Sergeant wrote: > > I missed this in the sequence spec <http://clojure.org/sequences>: When > seq is used on native Java arrays, changes to the underlying array will be > reflected in the seq - you must copy the source array to get full > immutability. > > I understand the rationale, still quite shocking. > > Ambrose > > On Wed, Oct 22, 2014 at 3:26 PM, Jozef Wagner <jozef....@gmail.com > <javascript:>> wrote: > >> Yes, seqs are presented as persistent collections, so this situation >> is quite unfortunate. But in the case of seq over mutable array, I >> think practical/performance reasons win over the correctness, which >> would require caching of realized items. > > As another poster noted, you can get caching of realized items if you really really want it, by using (map identity the-array). And if you want a snapshot at a particular time you had the array, regardless of how much later a particular sequence item will be first consumed, you can copy it upfront (with (into [] the-array), or just another array and System/arraycopy and don't let a reference to the new array escape). Although, mutation *while* you're taking the snapshot is harder to deal with. You and the potential mutator would have to agree on an object (say, the array itself) to lock. Once you have an immutable object in Clojureland though you can dispense with explicit locking and use the STM, atoms, and suchlike.
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