2010/4/30 Rich Hickey <richhic...@gmail.com>: > > On Apr 29, 2010, at 4:21 AM, ataggart wrote: > >> I know it won't matter, but for posterity if nothing else... >> >> Functions named contains-key? and contains-val? would make a lot more >> sense to me than the current contains? and new seq-contains?. Anyone >> looking at contains-val? should expect it to be O(n). The only >> effective difference would be that the test value for contains-val? is >> consistently a single value rather than a [key value] tuple for maps. >> > > > I disagree. > > People don't consider sets, vectors, arrays or strings to have 'keys'. But, > like maps, they all support fast lookup of some sort. > > Would contains-val? be fast for sets? As a user of sets, I consider them > collections of values, and I absolutely would reach for contains-val? in any > library that had it, for use with sets. If so, and I used contains-val?, and > I moved code from using sets to maps (happens frequently), or vectors (also > happens) my perf would suddenly stink. If not fast on sets, why not? The > reason isn't supported by the name. > > The mismatch with the seq values of maps is also disconcerting for something > that would purport to be sequential, as the things returned by (seq amap) > are key+value pairs. > > Just because you wouldn't reach for contains? for use with a known vector > doesn't mean your code, or other code built on the abstraction, won't end up > calling it with a vector. And don't think you never use contains? on a > vector/array - you rewrite it every time you write (if (and (<= 0 i) (< i > (count v))) ...) > > 'contains?' and 'get' abstract over fast lookup. They are polymorphic on the > collection type and on the nature of the looked-up thing. For maps the > looked-up thing is a key, for sets: a value, for vectors, strings and > arrays: an index. Calling it contains-key? doesn't make them the same, nor > add any value. > > In Clojure, 'contains?' is about 'get' succeeding. Nothing more or less. It > is not a rummager.
While it sounds soo evident now that you say that explicitly ( the contains? / get pair ), it may be good to reflect that in the docs of the functions rather than just keep this knowledge here ? > > (if (contains? coll x) > (get coll x) > (plan-b)) > > Renaming contains? is not on the table. For people that understand its > relationship with get, it makes perfect sense (and I don't think I'm the > only one :). And there is a lot of client code. And no one has come up with > a better name that doesn't include caveats. contains? is internally > consistent, is unfamiliar. > > I do understand that this use of the word differs from that used in e.g., > Java. But I'll make the same argument to Java devs that I do to the Lispers, > who have seen many more of their prized words repurposed in Clojure (assoc, > loop, do et al): > > The words can't mean the same thing forever without trapping us in the > same semantics forever, and there are only so many good words. > > Everyone has to realize that this level of polymorphism in Clojure is > unusual. I haven't seen a library with equivalents to get and contains?. > Heck, in Java, Maps aren't even collections! So, should we adopt their > nomenclature because it is familiar? > > I agree that contains?'s behavior on vectors is confusing for newcomers. > That's not a reason for it to be different. And that people need a way to do > that rummaging job. They of course can, with 'some'. But I also agree that > 'some', being a higher-order function, would not necessarily be the tool > newcomers would consider for the job of rummaging for a value. Perhaps it's > a good first lesson, as they are not going to find filter-val etc either. > > So, I pulled in 'includes?' from contrib and renamed it seq-contains? > > The only options for right now are: > > A) I remove seq-contains? > B) I rename seq-contains? > > I'm inclined towards A so we can all stop wasting time and energy on this > unnecessary function. > > Rich > > -- > 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 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
