On Mar 8, 3:59 pm, Timothy Baldridge <tbaldri...@gmail.com> wrote: > If in a namespace I bind a var: > > (def foo 3) > > And then later on in my program re-bind that var: > > (def foo 1) > > Will all parts of my program instantly see that update? How is it > possible to have any sort performance when we're basically having a > namespace function lookup for every single function call? > > Thanks for the help, > > Timothy > > -- > “One of the main causes of the fall of the Roman Empire was > that–lacking zero–they had no way to indicate successful termination > of their C programs.” > (Robert Firth)
That's not a binding, it's a def - they are different things. And yes, it slows things down a bit, so in 1.3 the default is to not support rebinding (though re-def'ing is still supported). But are you really asking how it's possible to have "any sort of performance" because a function call requires a pointer dereference? #'foo is a var whose current value is 3; #'first is a var whose current value is clojure.core/first. The compiler knows you're referring to #'first, and doesn't have to do any lookups to get to the pointer; it does a single deref to get the value of that pointer, just like it does to see what value is held in a function parameter (since those are passed by pointer). This is not that expensive. By the way, re-def'ing at runtime is a pretty bad code smell. If you're actually doing this, look into whether you can improve your code somehow, eg with one of: binding, atom/ref, or a closure capturing the value you want to "set". -- 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
