On Tue, Sep 25, 2012 at 5:10 AM, Nahuel Greco ngr...@gmail.com wrote:
I can't find the documentation for this behaviour:
(let [{x :b :as y} '(:a 1 :b 2)] [x y])
;= [2 {:a 1, :b 2}]
It seems as if the list in the init-expr is converted first to an
associative structure and then destructured.
But that behaviour doesn't seems to be documented, the map destructuring
documentation only talks
about destructuring of associative structures, and also there is nothing
about binding the :as expression
to the resultant associative structure instead of the initial init-expr.
Is this documented somewhere? Is an intended behaviour assured to be present
in the future Clojure
versions?
TL;DR: Intentional. Since 1.2.0.
This behavior was added in Clojure 1.2.0, the changes.txt for that release says:
== 2.3 Destructuring Enhanced ==
If you associatively destructure a seq, it will be poured
into a map first:
(defn foo [ {:keys [a b c]}]
[a b c])
(foo :c 3 :b 2)
= [nil 2 3]
But, I didn't see a reference to this behavior on the page on
clojure.org where special forms and destructuring are discussed [1].
[1]: http://clojure.org/special_forms#Special Forms--(let [bindings* ] exprs*)
// Ben
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