A list/seq (not a vector) which is destructured as a map will be first read
into a map as by (apply hash-map the-seq)
This curiosity exists so the "keyword argument" idiom works:
(defn my-options [_ & {:keys [a b] :as options}]
options)
=> #'user/my-options
(my-options nil :a 1 :b 2 :c 3)
=> {:c 3, :b 2, :a 1}
(my-options nil :a 1 :b 2 :c)
IllegalArgumentException No value supplied for key: :c
Keyword arguments have in general fallen out of favor (they were more
idiomatic in Clojure's early days), so you may not see this as often.
Generally people just pass an option map unless the function is meant
purely for "easy" interactive use (vs "simple" programmatic use). This is
because it's more difficult to call a keyword-argumented function correctly
when the keyword arguments are not literals.
On Friday, January 6, 2017 at 4:54:52 PM UTC-6, John Gabriele wrote:
>
> I've used associative destructing in the usual fashion:
>
> some-app.core=> (def m {:a 1 :b 2})
> #'some-app.core/m
>
> some-app.core=> (let [{:keys [a b]} m] (str a "-" b))
> "1-2"
>
> but what is going on here:
>
> some-app.core=> (def li '(:a 1 :b 2))
> #'some-app.core/li
>
> ;; Wat?
> some-app.core=> (let [{:keys [a b]} li] (str a "-" b))
> "1-2"
>
> I didn't think lists were associative... As in:
>
> some-app.core=> li
> (:a 1 :b 2)
>
> some-app.core=> (associative? li)
> false
>
> ;; So this is expected:
> some-app.core=> (let [{a 1 b 3} li] (str a "-" b))
> "-"
>
> some-app.core=> (def v [:a 1 :b 2])
> #'some-app.core/v
>
> ;; ...as is this (since vectors *are* associative):
> some-app.core=> (let [{a 1 b 3} v] (str a "-" b))
> "1-2"
>
>
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