Kevin Kleinfelter <kleinfelter.gro...@gmail.com> wrote:
> Can someone help me get un-stuck with a problem of using class in a case?
>
> This returns true, as I expect:
> (= (type "x") java.lang.String)
>
> This returns an error, and I'd hoped it would print STRING:
> (case (type "x")
> class java.lang.String (println "STRING")
> class java.lang.Long (println "NUM"))
>
> Because the error said "No matching clause: class java.lang.String", I
> thought maybe this would be better, but if gave the same error:
> (case (type "x")
> class java.lang.String (println "STRING")
> class java.lang.Long (println "NUM"))
>
> Is in not possible to match on class in a case?
Correct, because the test expressions have to be compile-time constants.
Also, "class java.lang.String" isn't valid Clojure syntax for an
expression. Just "java.lang.String" evaluates to the class with that
name, but the test expressions aren't evaluated.
I think the most common approach for this scenario is to use condp:
(condp instance? "x"
java.lang.String "STRING"
java.lang.Long "LONG")
Hope that helps
John
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