I think this is not a bug in disj. disj takes a *set* and an element
as input. nil is the empty seq, which is different from the empty set
#{}. The fact that clojure.set functions work at all on things other
than bona fide sets is, in Rich's words, "an implementation artifact
and not a promise of the interface".
-Jason
On Jan 29, 6:42 am, ntu...@googlemail.com wrote:
> If its left argument is nil, "intersection" throws a NPE (Clojure rev. 1235):
>
> user=> (set/intersection nil #{1})
> java.lang.NullPointerException (NO_SOURCE_FILE:0)
> user=> (.printStackTrace *e)
> java.lang.NullPointerException (NO_SOURCE_FILE:0)
> at clojure.lang.Compiler.eval(Compiler.java:4186)
> at clojure.core$eval__3830.invoke(core.clj:1647)
> at clojure.main$repl__5568$fn__5586.invoke(main.clj:148)
> at clojure.main$repl__5568.doInvoke(main.clj:145)
> at clojure.lang.RestFn.invoke(RestFn.java:426)
> at clojure.main$repl_opt__5610.invoke(main.clj:208)
> at clojure.main$main__5645$fn__5647.invoke(main.clj:295)
> at clojure.main$main__5645.doInvoke(main.clj:289)
> at clojure.lang.RestFn.invoke(RestFn.java:402)
> at clojure.lang.Var.invoke(Var.java:332)
> at clojure.lang.AFn.applyToHelper(AFn.java:172)
> at clojure.lang.Var.applyTo(Var.java:453)
> at clojure.main.main(main.java:39)
> Caused by: java.lang.NullPointerException
> at clojure.core$disj__3445.invoke(core.clj:915)
> at clojure.core$reduce__3173$fn__3176.invoke(core.clj:549)
> at clojure.core$reduce__3173.invoke(core.clj:547)
> at clojure.set$difference__5658.invoke(set.clj:19)
> at clojure.set$intersection__5661.invoke(set.clj:24)
> at user$eval__259.invoke(Unknown Source)
> at clojure.lang.Compiler.eval(Compiler.java:4175)
> ... 12 more
> nil
> user=> (msg/select-messages msgs nil "OR" nil)
> nil
> user=> (set/intersection #{} nil)
> #{}
>
> The same is true for clojure.set/difference and everything else that
> uses clojure.disj with nil for the first parameter.
>
> Cheers,
> nt
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