> The following code shows surprising behavior related to using protocol
> functions in higher order functions. I sort of understand the reason
> wrapped-x first fails is that calling extend-protocol in a sense
> redefines the x protocol function. I can't decide if I think this is a
> bug or just the way protocols work. I am curious what others think.
>
> -David
>
> ====
>
> (defprotocol Foo
> (x [this arg]))
>
> (defn wrap [f]
> (fn [& args]
> (apply f args)))
>
> (def wrapped-x (wrap x))
>
> (extend-protocol Foo
> String
> (x [this arg]
> (str this arg)))
>
> (wrapped-x "hello" "joe")
> ;; -> No implementation of method: :x of protocol: #'user/Foo found
> for class: java.lang.String
>
> (def wrapped-x (wrap x))
>
> (wrapped-x "hello" "joe")
> ;; -> "hellojoe"
I think not a bug. If you want indirection in your wrapper, you can ask for it,
e.g.:
(defn wrap [f]
(fn [& args]
(apply @f args)))
(def wrapped-x (wrap #'x))
Stu
Stuart Halloway
Clojure/core
http://clojure.com
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