Can I change the title to:
"Duplicate key error handling feature in hash-sets" ?
I was using the '#' thinking it was short for a hash-map, rather than
a hash-set.
Clojure has more data structures available than I'm used to working
with.
So thanks for the error handling.
Tim
On Jun 25, 9:37 am, Stuart Halloway <stuart.hallo...@gmail.com> wrote:
> I think there are two important considerations in favor of how it works now:
>
> (1) The "common case" presumptions (which admittedly may need to be learned).
>
> (2) The need for both flavors. If there wasn't a flavor that rejected
> duplicate keys, somebody would surely ask for it.
>
> Add to these considerations the names of the functions already in play, and
> you get the implementation you see.
>
>
>
> > 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.
>
> > O< ascii ribbon campaign - stop html mail -www.asciiribbon.org
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