On Mon Mar 26 15:15 2012, Cedric Greevey wrote:
> > What you're running into is the overhead of get the root value of vars
> > like swap! and move-up!. The only way to avoid this is use something
> > like definline.
>
> I thought that in 1.3 those had been made much faster to access if
> they didn't have ^{:dynamic true} applied to them?As of Clojure 1.3, by default, vars only have a root value that exists globally. When you tag a var as being ^:dynamic, it is allowed to have thread-local bindings. However, remember you can always change the value of a var: (defn foo [] :foo) ; evaluates to :foo (defn printfoo [] (println (foo))) (printfoo) ; prints :foo (defn foo [] :bar) ; evaluates to :bar (printfoo) ; prints :bar As a result, whenever you use a var in a function, the latest value is retrieved from the var. This ensures that your function always sees the latest value that is assigned to the var. As far as I know, the only way to avoid this is to use compile-time inlining of the method body. You can do this with definline: (definline foo [] :foo) ; evaluates to :foo (defn printfoo [] (println (foo))) (printfoo) ; prints :foo (definline foo [] :bar) ; evaluates to :bar (printfoo) ; still prints :foo! As you can see, definline can make code much harder to understand. It only really makes sense in tight loops where hot functions are being repeatedly invoked. Otherwise, I doubt vars add significant overhead for most Clojure code. Sincerely, Daniel
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