I guess here is the correct answer, because:
Because $a is not always an array and you use $a[$k].
array_merge_recursive does indeed merge arrays, but it converts values with duplicate keys to arrays rather than overwriting the value in the first array with the duplicate value in the second array, as array_merge does.
other aswers are not recursives or not simple.
So, here is my answer: your answer without bugs:
function array_extend(array $a, array $b) {
foreach($b as $k=>$v) {
if( is_array($v) ) {
if( !isset($a[$k]) ) {
$a[$k] = $v;
} else {
if( !is_array($a[$k]){
$a[$k]=array();
}
$a[$k] = array_extend($a[$k], $v);
}
} else {
$a[$k] = $v;
}
}
return $a;
}
And my answer with ternary operator:
function array_extend(array $a, array $b){
foreach($b as $k=>$v)
$a[$k] = is_array($v)&&isset($a[$k])?
array_extend(is_array($a[$k])?
$a[$k]:array(),$v):
$v;
return $a;
}
Edit: And a bonus one with as many arrays you want:
function array_extend(){
$args = func_get_args();
while($extended = array_shift($args))
if(is_array($extended))
break;
if(!is_array($extended))
return FALSE;
while($array = array_shift($args)){
if(is_array($array))
foreach($array as $k=>$v)
$extended[$k] = is_array($v)&&isset($extended[$k])?
array_extend(is_array($extended[$k])?
$extended[$k]:array(),$v):
$v;
}
return $extended;
}