On Sunday, February 22, 2015 at 12:52:04 PM UTC-5, Timur wrote:
>
> Hi everyone,
>
> I have the following question regarding the defmultis of clojure:
>
> (defmulti create-fact
> (fn [item-vector] (do
> (print item-vector)
> (first item-vector))))
>
> (defmethod create-fact [:a] [item-vector]
> (str "a"))
>
> (defmethod create-fact [[:a "safs"]] [item-vector]
> (str "safs"))
>
>
> (mapv create-fact {:a "safs"})
>
>
> Dispatch function is not called in this case and return is "safs" so the
> matching key is [[:a "safs"]]. I except it to be :a, why is that [[:a
> "safs"]]?
>
Not sure why your print is not working, but it's otherwise behaving as
expected. Treating a map as a seq produces a seq of map-entry objects,
rather than alternating keys and values. (You can use mapcat instead of
map/mapv to get alternating keys and values though.) So this is calling
create-fact once, with a parameter of [:a "safs"] (actually a map-entry
object, but prints like and can often be used as a two-element vector, and
to some extent vice versa, for instance (into {} [[:a 1][:b 2]]) produces
{:a 1 :b 2}).
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