Question

Look at this code:

$a = array('1'=>'1');
$b = array(''=>'');

var_dump(array_merge($a,$b));

the output seems really strange to me:

array(2) {
  [0] =>
  string(1) "1"
  '' =>
  string(0) ""
}

Ok, I’ve changed $a into this: $a = array('k'=>'v'); and the output became more predictable:

array(2) {
  'k' =>
  string(1) "v"
  '' =>
  string(0) ""
}

The question is: why the hell the key of the first element is 0 in the first example?

edit:

var_dump($a);
array(1) {
  [1] =>
  string(1) "1"
}

Answer 1

Values in the input array with numeric keys will be renumbered with incrementing keys starting from zero in the result array.

http://php.net/array_merge

Yes, it’s an idiosyncrasy of PHP to treat numeric string values as numeric values in this case. You may want to use $a + $b instead.