Ah! Thank you, Francis! And sorry for the belated reply!
I ran into a terse example of it at
<https://clojure.org/guides/destructuring#_associative_destructuring> (see
"(def options '(:debug true))") and was scratching my head. Now that you
explained it though, I remembered seeing an explanation of it somewhere.
Turns out I'd forgotten reading about that bit of magic in the "Clojure
Programming" book (p.35).
-- John
On Friday, January 6, 2017 at 7:36:51 PM UTC-5, Francis Avila wrote:
> 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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