One possibly confusing titbit I came across recently relates to how Clojure
handles destructuring of variable-length argument lists. The essence is
that the destructuring form can appear to influence the 'shape' of the
collection of arguments. Here is what I mean:
take nothing off the head of the vector, then put all remaining elements
into a vector c:
user=> (let [[& [:as c]] [:one "one" :two "two"]] (seq c))
(:one "one" :two "two")
take nothing off the head of the vector, then put all remaining elements
into a map c:
user=> (let [[& {:as c}] [:one "one" :two "two"]] (seq c))
([:one "one"] [:two "two"])
Notice how the structure of 'c' has changed due to the destructuring form,
even though in both cases it refers to the whole collection. Digging down
into this a bit, it looks like this depends on the type of the collection
being destructured:
user=> (let [{:as c} [:one "one" :two "two"]] (seq c))
(:one "one" :two "two")
user=> (let [{:as c} (seq [:one "one" :two "two"])] (seq c))
([:one "one"] [:two "two"])
I can see why this is necessary for multiple-args destructuring to work,
but I think my small mind finds this 'automatic marshalling' of
lists-or-seqs into maps a bit confusing. Maybe my only real problem is the
destructuring of vectors as maps, which somewhat 'works' in the above
example, but isn't really consistent. Any thoughts?
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