Cheers, Justin - I'd forgotten that (and just thought that vector-as-map
destructuring was broken - but this would explain why it is different from
other seqables.)
Doug
On Tuesday, August 28, 2012 3:12:43 PM UTC+1, Justin Kramer wrote:
>
> Vector-as-map destructuring makes sense when you consider that vectors are
> associative: they map index to value.
>
> (let [{a 1 b 3 :as c} [:a 1 :b 2]] [a b c])
> => [1 2 [:a 1 :b 2]]
>
> Justin
>
> On Tuesday, August 28, 2012 8:30:58 AM UTC-4, Douglas Orr wrote:
>>
>> 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?
>>
>
--
You received this message because you are subscribed to the Google
Groups "Clojure" group.
To post to this group, send email to clojure@googlegroups.com
Note that posts from new members are moderated - please be patient with your
first post.
To unsubscribe from this group, send email to
clojure+unsubscr...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/clojure?hl=en
