Question

Given an associative array like the following,

$field_defaults = array(
  'id' => 0,
  'name' => 'new item',
  'desc' => '',
  'parent_id' => 0,
);

can I rely on array_keys() returning the keys in the order they were specified? Or, more precisely, since arrays in PHP seem to have a stable order, as per this answer, are the keys returned by array_keys() in the same order as they appear in the input array? The manual page doesn’t give any hints.

When I try this, they seem to respect the original order, but I would like to be able to rely on that behaviour.

Answer 1

TL;DR: Theoretically you can’t count on it; for practical purposes IMO you can.

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Since the docs do not guarantee the ordering then technically the correct answer would be “no, you can’t count on that”.

_{That’s because theoretically the developers could have chosen to reserve themselves the option of changing the implementation at a future date so that it does not honor the existing order any more (perhaps to improve performance, or to gain some other benefit).}

Now as a practical matter, we know that the current implementation honors the ordering — PHP arrays are ordered containers (there is a linked list of values among other things) — and this is something you wouldn’t ever expect to change.

If it did, the change would hint to a corresponding significant change in the internal implementation of arrays and that would in turn be likely to break lots of other code too. I don’t see it happening any time soon.