[development] += on arrays

Larry Garfield larry at garfieldtech.com
Wed Jan 18 02:42:21 UTC 2006

On Tuesday 17 January 2006 20:28, Jeremy Epstein wrote:
> First of all, you should remember this fundamental difference between
> array_merge() and the array + operator:
> " Don't forget that numeric keys will be renumbered! ... If you want
> to completely preserve the arrays and just want to append them to each
> other, use the + operator."
> (from http://www.php.net/manual/en/function.array-merge.php)
> Personally, I find that the re-indexing behaviour of array_merge() is
> often not what I want, so I'm finding that I use the + operator more
> and more.
> Also, consider these two examples:
> $array1 = array_merge($array1, $array2);
> $array1 += $array2;
> In the first example (assuming that the keys aren't numeric), $array2
> is guaranteed to have all its values preserved; in the second example
> (no matter what type the keys are), $array1 is guaranteed this. So...
> On 1/18/06, Larry Garfield <larry at garfieldtech.com> wrote:
> > So... array_merge($a, $b) favors $a, while $a += $b favors $b?  Wouldn't
> > that mean that
> >
> > array_merge($a, $b) == $b += $a
> It's the other way around, Larry. :-) But the two operations are only
> equivalent IF there are no numeric keys! If there are, then
> array_merge() behaves differently (and stupidly, IMO).

Ah ha.  So I was backward but had the right idea. :-)  The direction I'm going 

> On a related note: perhaps we should agree on a recommended way (i.e.
> one of the above two ways) of merging arrays in Drupal? I'd like to
> see the + operator encouraged, as it's more predictable, and
> (according to chx) is also faster. But I don't know that we can outlaw
> array_merge() altogether (as we did with array_key_exists() recently)
> as there may still be times when it's needed, since it is a bit
> different to the + operator.

Exactly.  If array_merge($a, $b) == $b += $a iff $a and $b are strictly 
associative arrays, and += is substantially faster, and Drupal uses 
associative arrays a LOT, it seems like this is a good language-level 
optimization to make and recommend.

Larry Garfield			AIM: LOLG42
larry at garfieldtech.com		ICQ: 6817012

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