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)
They are allowed in other contexts, where the data could come from anywhere:
; 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. :-)
Stu
> On Fri, 25 Jun 2010 15:36:31 +0200
> Michael Wood <[email protected]> wrote:
>
>> On 25 June 2010 12:27, Tim Robinson <[email protected]> wrote:
>>> I tried Clojure via Githhub today.
>>>
>>> Anyone notice this bug that hadn't existed in Version 1.1
>>>
>>> user=> #{:item1 {:a "A" :b "B"} :item2 {:a "A" :b "B"}}
>>> java.lang.IllegalArgumentException: Duplicate key: {:a "A", :b "B"}
>>
>> You're trying to put duplicate values into a set.
>
> So? Most places, putting a value that's already in a set into the set
> is a nop. Even in clojure that exhibits the above behavior:
>
> user=> #{:a :a}
> java.lang.IllegalArgumentException: Duplicate key: :a
> user=> (set [:a :a])
> #{:a}
> user=> (conj #{:a} :a)
> #{:a}
> user=>
>
> Apparently, duplicate keys in sets are only disallowed in set
> literals. Arguably, that must be a mistake on the users part, but
> it sure seems to clash with the behavior of sets elsewhere.
>
> <mike
> --
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