I think Mailbox app might have messed with the quoting in my last reply. I hope it makes sense.
I'm not suggesting that the function be changed - Clojure's API compatibility between versions is amazing and a fine example of great engineering. Reading other people's input on this thread has made it clear to my what I find surprising - rand-nth does not behave like `first` when called on an empty collection, and in my mind asking for the first element of a sequence and asking for a random element of that sequence are similar operations. I do see the point of view that nth throws on out-of-bounds access, so rand-nth should too, but in that case I would expect rand-nth to throw too. I would like to see that subtlety mentioned in the doc string. Thanks Alex & all! On Wed, Sep 30, 2015 at 3:14 PM, Alex Miller <a...@puredanger.com> wrote: > 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. -- 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.
