On Wed, Aug 18, 2010 at 11:09 AM, Brian Hurt <bhur...@gmail.com> wrote: > Consider the following bit of code: > > (let [ x (new java.lang.Boolean false) ] (if x "trouble" "ok"))
I consider the fact that Boolean has a public constructor a bug. It can only ever represent 2 values. However, if you do (let [x (java.lang.Boolean/getBoolean "false")] (if x :trouble :ok)) you're fine, which obviously isn't helpful in your situation. > As you might guess from the fact that I'm calling it's a trick question, the > above code returns "trouble", not "ok". From experimentation, it looks like > clojure's if takes the second branch if the value is nil or referentially > equal to java.lang.Boolean/FALSE. If you have a boolean object which is not > referentially equal to Boolean/FALSE, but still holds the value false, this > is treated as true by Clojure. > > The problem is, I'm not 100% sure if this is a bug or not. The problem is > nil-punning. The if statement can't rely on the test expression evaluating > to a boolean. Which means to make this work correctly, if statements would > have to do an instanceof test (to see if the object was a Boolean), then a > cast and a call to .booleanValue to get the boolean value. Which is way > more expensive than a quick nil test and referential equality test. > > This is, however, more than a little bit surprising and depressing. > Somewhere, in my 10K lines of clojure code, boolean values are getting boxed > in exactly that way. I've fixed the current problem (dropping in a call to > .booleanValue in the test), but having if statements that can fail makes me > paranoid. > > Brian > > -- > 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 -- http://www.apgwoz.com -- 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
