- var_dump: documentation ( source)
- array_merge: documentation ( source)
<?php
$array1[0] = 'zero';
$array1[1] = 'one';
$array2[1] = 'one';
$array2[2] = 'two';
$array2[3] = 'three';
var_dump($array1 + $array2);
var_dump(array_merge($array1 + $array2));