> Also, given the implementation above, why does the array have to be
ksorted
> correctly to count? Specifically, why isn't this array considered vector
> like?
> $arr = [
> 1=> 1,
> 0=> 0,
> ];
I suppose the question would be, given that array (or a similar
out-of-order array), should is_vectorlike afford you the expectation that
in a foreach loop:
foreach ($arr as $i => $v) {
// do something
}
that (within the length of the array) the value $arr[$i + 1] has not yet
been processed by the code in the loop, and is also the next item to be
processed.
Or maybe more succinctly, should is_vectorlike guarantee that items are
iterated over in order?
On 5 May 2017 at 22:19, Ryan Pallas <derokor...@gmail.com> wrote:
> On Tue, May 2, 2017 at 3:13 AM, Jesse Schalken <m...@jesseschalken.com>
> wrote:
>
> > Related to the optimisation made by Sara Golemon here:
> > https://github.com/php/php-src/commit/c74bc87c74f48bc55541b3bf2fc67d
> > 595f58a3b5
> >
> > I often define a function like this, which checks if an array is "vector
> > like" i.e. has keys 0,1,2..N:
> >
> > function is_vectorlike(array $a): bool {
> > $i = 0;
> > foreach ($a as $k => $v) {
> > if ($k !== $i++) {
> > return false;
> > }
> > }
> > return true;
> > }
> >
> > The problem is that this function is O(n), but in PHP7 an array that is
> > vector-like is likely to be packed and without holes (HT_IS_PACKED(x) &&
> > HT_IS_WITHOUT_HOLES(x)), in which case it is known to be vector-like
> > without needing to iterate over it, but PHP code can't check for this
> (nor
> > should it be able to, since it's really an implementation detail).
> >
> > Would it be a good idea to define this is_vectorlike() function in the
> PHP
> > runtime, so it can short circuit to return true on packed arrays without
> > holes? The above code would be a suitable polyfill.
> >
>
>
> I just read this thread and am wondering what exactly is the use case? Like
> are you going to do something if it is vector-like, and do something
> different (or not do anything at all) if it's not vector-like? I mean, if
> you have to crawl it, and need a vector, why not just call array_values and
> guarantee you have a vector?
>
> Also, given the implementation above, why does the array have to be ksorted
> correctly to count? Specifically, why isn't this array considered vector
> like?
> $arr = [
> 1=> 1,
> 0=> 0,
> ];
>
> Wouldn't the following be a better test?
> function is_vectorlike(array $a): bool {
> $l = count($a);
> for (i=0; $i<$l, $i++) {
> if (!array_key_exists($i, $a)) {
> return false;
> }
> }
> return true;
> }
>
