On Tue, Dec 30, 2008 at 8:38 PM, Rich Hickey <richhic...@gmail.com> wrote: > There's simply no value for Clojure to add to a simple mutable box. > Clojure does provide the tools for low-level mutation - access to > Java. You can wrap that in whatever functions/macros you like. >
There's no way to use the @ dereferencing syntax for a custom mutable box, right? The sample I gave would be considerably harder to read if you had to use (box-ref u) instead of @u everywhere. > OTOH, atom-set just invites the read-modify-write race conditions > swap! was meant to avoid. Yes, but not every write to an atom is going to be a read-modify-write kind of change, which is why it feels odd to always be limited to swap!. Since my examples emphasized the "simple mutable box" benefits of having atom-set, and you didn't find that compelling, let's go back to the discussion earlier in this thread about using an atom to maintain a counter that increments to generate unique IDs. You've already stated that this is one of the uses that is a good fit for atom. It would be entirely reasonable to want to, under certain conditions, to reset the counter to 0. When you reset to 0, that's just a straight write. Having to say (swap! counter (constantly 0)) feels convoluted, and somewhat obscures the fact that this change is not dependent on the previous state of the atom. Furthermore, by having to represent this reset as a swap, the counter reset might not happen as quickly as one would like. If there is a lot of contention and other threads are in the process of incrementing the counter, the reset might fail to go through for a while, because the value is frequently changed by other threads between the unnecessary read and the write of 0. An atom-set would not only reflect the intentions of the code better, but would provide better performance for the times where a read is irrelevant to the value being written. Yes, atom-set invites a certain potential for misuse, but atoms already require a certain degree of care. --~--~---------~--~----~------------~-------~--~----~ 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 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 -~----------~----~----~----~------~----~------~--~---
