AFAIK treating kv lists as maps in destructuring was only introduced to
support kwargs destructuring, hence why it's not supported for vectors.
On 02/01/17 18:00, Sean Corfield wrote:
This one had me scratching my head a bit too… here’s what I _/think/_
is going on:
First off, note that the most usual way to use the :keys destructuring
is with a map:
(let [{:keys [opt1]} {:opt1 true}] [opt1]) ==> [true]
As you noted, the guide explicitly calls out “lists” and in this case
you are passing a literal list:
(let [{:keys [opt1]} '(:opt1 true)] [opt1]) ==> [true]
You’d also get the same answer with:
(let [{:keys [opt1]} (list :opt1 true)] [opt1]) ==> [true]
But in this code, you have a vector, not a list:
(let [{:keys [opt1]} [:opt1 true]] [opt1]) ==> [nil]
If you turn your vector into a sequence, it _/does/_ work:
(let [{:keys [opt1]} (seq [:opt1 true])] [opt1]) ==>
[true]
So it allows lists and sequences but not vectors here.
I’d be interested to know why vector isn’t treated the same as list /
sequence here...?
Sean Corfield -- (970) FOR-SEAN -- (904) 302-SEAN
An Architect's View -- http://corfield.org/
"If you're not annoying somebody, you're not really alive."
-- Margaret Atwood
On 1/2/17, 2:41 AM, "mattias w" <clojure@googlegroups.com
<mailto:clojure@googlegroups.com> on behalf of matti...@gmail.com
<mailto:matti...@gmail.com>> wrote:
Could someone explain why the first doesn't work and the 2nd does?
(let [{:keys [opt1]} [:opt1 true]] [opt1]) ==> [nil]
(let [{:keys [opt1]} '(:opt1 true)] [opt1]) ==> [true]
According to http://clojure.org/guides/destructuring
"Associative destructuring also works with lists of key-value pairs
for keyword-arg parsing."
If I read the definition literally, I see, it says "lists" and not
"sequences", so the behaviour is correct, so maybe a better question
is why the definitions isn't
"Associative destructuring also works with sequences of key-value
pairs for keyword-arg parsing."
It this specific case, when you destructor the args, it looks like a
vector, but internally it is a list, so it works.
Happy New Year!
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