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; }
