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Date: Thu, 23 May 2019 21:18:55 +0200
Message-ID: <CAF+90c9bcOGpMBTpM2hSLbfZOkYOqPiCoZngfe4c5KBa+1+KSQ@mail.gmail.com>
To: Dik Takken <d.takken@xs4all.nl>
Cc: "G. P. B." <george.banyard@gmail.com>, PHP Development <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000016eb5058992f538"
Subject: Re: [PHP-DEV] Calling array_merge / array_merge_recursive without arguments
From: nikita.ppv@gmail.com (Nikita Popov)

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On Thu, May 23, 2019 at 9:02 PM Dik Takken <d.takken@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

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