On Jun 18, 1:25 pm, Adam Blinkinsop <bli...@acm.org> wrote: > I'm looking through the primitives that Clojure has for STM with refs, and > it seems nice and minimal, except for these two functions, which I can't > tease apart. From the documentation, > > *(ref-set ref val)* > > Must be called in a transaction. Sets the value of ref. Returns val. > > *(alter ref fun & args)* > > Must be called in a transaction. Sets the in-transaction-value of ref to: > > > (apply fun in-transaction-value-of-ref args) > > and returns the in-transaction-value of ref. > > Does ref-set not set the "in-transaction-value"? It looks like the only > difference is the signature, and that can't be right.
Looks to me like they are analogous to reset! and swap! on atoms. (swap! atom fn & args) is shorthand for (reset! atom (fn @atom & args)) with the added, crucial ingredient of atomicity; nothing else can change the atom in between the deref and the reset if you use swap!. With transactions, the difference is less stark. It just saves you some typing: (alter ref fn & args) replaces (ref-set ref (fn @ref & args)), or maybe (ref-set ref (fn (ensure ref) & args)). Atomicity is unaffected since the transaction as a whole is committed atomically, transactions are thread-local, and the in-transaction value of ref is used in all three cases. --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
