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Date: Tue, 2 May 2017 19:13:49 +1000
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Subject: Add is_vectorlike($array) function
From: me@jesseschalken.com (Jesse Schalken)

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Related to the optimisation made by Sara Golemon here:
https://github.com/php/php-src/commit/c74bc87c74f48bc55541b3bf2fc67d595f58a3b5

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.

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