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On Thu, May 23, 2019 at 9:02 PM Dik Takkentakken@xs4all.nl> wrote: > On 21-05-19 10:29, Nikita Popov wrote: > > This one makes sense in theory, because array_map(null, ...$arrays) is a > > way to perform a zip operation in PHP. Unfortunately there is an ugly > > special case if there is only a single array, which makes this not > actually > > usable in practice, unless you know that there are at least two arrays. > As > > such, accepting zero arrays wouldn't be very useful unless we also want > to > > fix that issue (PHP 8 maybe?) > > Ah, I overlooked that edge case. Indeed, array_map() would require more > fixing than I anticipated. I guess it is out of scope for the type of > fix we are discussing. > > >> array_diff() & friends > > > > array_intersect() & friends > > > > > > These look like good candidates for allowing a single arg. > > For array_intersect(), I was actually considering to allow zero > arguments. The use case I have in mind is to determine the common > elements in a set of zero or more arrays, like this: > > array_intersect(...$arrays) > > If that would just return an empty array when $arrays is empty, no > additional empty check is needed and the above would do what I > intuitively expect it to do. >Common intuition, but not mathematically sound. Assuming we're intersecting subsets of a certain universe U, then the intersection of no sets is U itself, not the empty set. (A useful intuition is that intersecting additional sets can only make the result smaller -- as such intersecting no sets at all yields the largest possible result.) Nikita

> On Thu, May 23, 2019 at 9:02 PM Dik TakkenYou are completely right, thanks for pointing that out. Regards, Dik Takkentakken@xs4all.nl> wrote: > >> For array_intersect(), I was actually considering to allow zero >> arguments. The use case I have in mind is to determine the common >> elements in a set of zero or more arrays, like this: >> >> array_intersect(...$arrays) >> >> If that would just return an empty array when $arrays is empty, no >> additional empty check is needed and the above would do what I >> intuitively expect it to do. >> > > Common intuition, but not mathematically sound. Assuming we're intersecting > subsets of a certain universe U, then the intersection of no sets is U > itself, not the empty set. (A useful intuition is that intersecting > additional sets can only make the result smaller -- as such intersecting no > sets at all yields the largest possible result.) > > Nikita >