rand-nth cannot return a random element if there are no elements to return, so I do not find this surprising. Returning nil would be an invalid answer in my opinion.
The rand-nth doc string implies that rand-nth will inherit the semantics of nth for the specified collection. nth will generally throw on an invalid index (and all indexes are invalid for an empty collection). For nil, the docstring for nth does not mention nil explicitly, so I would treat this as undefined behavior unless you consider it as a degenerate sequence. The code (in RT.nthFrom()) explicitly handles this case and effectively treats nil as an infinite indexed source of nils, rather than as an empty sequence. In my own opinion (but maybe not Rich's), it seems to make more sense to take the sequence interpretation and say that on nil, nth should throw instead. So that might be a valid ticket. I'm not sure what, if any, negative consequences would arise out of existing uses of nth that rely on this behavior though. Given the number of things built on nth, it may be impossible to change this even if it made sense to. Alex On Wednesday, September 30, 2015 at 6:38:49 AM UTC-5, Marc O'Morain wrote: > > Hi all, > > I was surprised by the fact that rand-nth thrown when called on an empty > collection - see http://dev.clojure.org/jira/browse/CLJ-925 > <http://www.google.com/url?q=http%3A%2F%2Fdev.clojure.org%2Fjira%2Fbrowse%2FCLJ-925&sa=D&sntz=1&usg=AFQjCNFpBhBI2wA5LnBRCiAP8oYyF5HdOg> > > This behaviour is strange, since passing nil to rand-nth returns nil, > whereas in my experience, other Clojure functions treat nil and empty > collections in the same way (compare with next/rest/first, etc). > > http://dev.clojure.org/jira/browse/CLJ-925 was marked as Completed > without comment – is this the intended behaviour? If so, would you accept a > patch to update the docstring to make it clear that the function will throw > an exception when passed an empty collection? > > Thanks, > > Marc > -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
