On Thu, Jul 9, 2009 at 4:19 PM, Richard Newman<[email protected]> wrote:
>
> Is there any particular reason why Fn doesn't implement IMeta?
Actually, it does.
user=> (instance? clojure.lang.IMeta (fn []))
true
What it doesn't support is changing the metadata after
creation:
user=> (with-meta (fn []) {:foo "bar"})
java.lang.UnsupportedOperationException (NO_SOURCE_FILE:0)
The reasons for this have to do with difficulties involved
in cloning a closure as would be necessary.
You can however set the metadata when you create a new
instance -- AFn takes a metadata map in its constructor.
There's no syntax supporting it directly, but you can get at
it from Java, gen-class, or proxy:
(def add
(proxy [clojure.lang.AFn] [{:i-has "metadata!"}]
(invoke [a b] (+ a b))))
user=> (add 2 5)
7
user=> ^add
{:i-has "metadata!"}
--Chouser
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