On Fri, 25 Jun 2010 10:31:57 -0400
Stuart Halloway <stuart.hallo...@gmail.com> wrote:
> Duplicate keys in maps/sets are disallowed in literals and factory functions,
> where data is generally literal & inline and therefore likely represents
> coder error:
>
> ; all disallowed
> #{:a :a}
> {:a 1 :a 2}
> (hash-map :a 1 :a 2)
> (hash-set :a :a)
Maps I can see being an error - you lose data in the process.
However, since you can plug variables of unknown provenance into
either the constructor or the literal, that's liable to create a nasty
surprise for someone at some point.
user=> (def a :a)
#'user/b
user=> (def b :a)
#'user/b
user=> (hash-set a b)
java.lang.IllegalArgumentException: Duplicate key: :a (NO_SOURCE_FILE:6)
user=> #{a b}
java.lang.IllegalArgumentException: Duplicate key: :a (NO_SOURCE_FILE:0)
user=>
> They are allowed in other contexts, where the data could come from anywhere:
It could come from anywhere in the two "forbidden" contexts as well.
> ; dumb, but these forms not generally called with a literal
> (set [:a :a])
> (into #{} [:a :a])
>
> I find this behavior consistent and easy to explain, but I was involved in
> the design conversation so maybe I have participant blindness. :-)
My initial reaction was "that's a bit odd, but probably a good idea."
However, given that I can use variables inside the literal and
constructor, I'm leaning the other way.
Or is (set [a b c]) idiomatic usage in this case, and (hash-set a b c)
or #{a b c} to be avoided?
<mike
--
Mike Meyer <m...@mired.org> http://www.mired.org/consulting.html
Independent Network/Unix/Perforce consultant, email for more information.
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