"array_intersect_ukey" will not work if $key_compare_func is using regular expression to perform comparison. "_array_intersect_ukey" fully implements the "array_intersect_ukey" interface and handles properly boolean comparison. However, the native implementation should be preferred for efficiency reasons.

<?php
$key_compare_func = function ($a, $b) {
    var_dump('a=' . $a. '; b=' . $b);
    
    if (strpos($b, '/') === 0) {
        return preg_match($b, $a) > 0 ? 0 : -1;
    }
    
    if ($a == $b) {
        $weight = 0;
    } else if ($a > $b) {
        $weight = 1;
    } else {
        $weight = -1;
    }
    
    var_dump('literal comparison: ' . $weight);
    
    return $weight;
};

$foo = ['aab' => '', 'bbb' => '', 'ccb' => '', 'abb' => ''];
$bar = ['/[a-z]b[a-z]/' => ''];
$buz = ['/c[a-z][a-z]/' => ''];

echo PHP_EOL . 'array_intersect_ukey' . PHP_EOL . PHP_EOL;

$subject = array_intersect_ukey ($foo, $bar, $buz, $key_compare_func);

echo PHP_EOL;

var_dump($subject);

echo PHP_EOL . '_array_intersect_ukey' . PHP_EOL . PHP_EOL;

$subject = _array_intersect_ukey($foo, $bar, $buz, $key_compare_func);

echo PHP_EOL;

var_dump($subject);

/**
 * @author Gajus Kuizinas <[email protected]>
 * @version 1.0.0 (2013 09 30)
 * @url https://gist.github.com/gajus/271ad5f36337a32a184c
 */
function _array_intersect_ukey (array $arr1, array $arr2, $key_compare_func) {
    $arr_matched = [];
    $arr_unmatched = [];
    
    $args = func_get_args();
    
    $key_compare_func = end($args);
    
    foreach ($arr1 as $k1 => $v1) {
        foreach ($arr2 as $k2 => $v2) {
            $diff = $key_compare_func($k1, $k2);
        
            //var_dump('k1=' . $k1 . ', k2=' . $k2 . ', diff=' . $diff);
            
            if ($diff === 0) {
                $arr_matched[$k1] = $v1;
            } else {
                $arr_unmatched[$k1] = $v1;
            }
        }
    }
    
    if (count($args) <= 3) {
        return $arr_matched;
    }
    
    array_splice($args, 0, 2, [$arr_unmatched]);
    
    return array_merge($arr_matched, call_user_func_array('_array_intersect_ukey', $args));
}

/*
array_intersect_ukey

string(12) "a=bbb; b=aab"
string(21) "literal comparison: 1"
string(12) "a=bbb; b=ccb"
string(22) "literal comparison: -1"
string(12) "a=abb; b=bbb"
string(22) "literal comparison: -1"
string(12) "a=aab; b=abb"
string(22) "literal comparison: -1"
string(22) "a=aab; b=/[a-z]b[a-z]/"
string(22) "a=abb; b=/[a-z]b[a-z]/"
string(22) "a=abb; b=/c[a-z][a-z]/"

array(0) {
}

_array_intersect_ukey

string(22) "a=aab; b=/[a-z]b[a-z]/"
string(22) "a=bbb; b=/[a-z]b[a-z]/"
string(22) "a=ccb; b=/[a-z]b[a-z]/"
string(22) "a=abb; b=/[a-z]b[a-z]/"
string(22) "a=aab; b=/c[a-z][a-z]/"
string(22) "a=ccb; b=/c[a-z][a-z]/"

array(3) {
  ["bbb"]=>
  string(0) ""
  ["abb"]=>
  string(0) ""
  ["ccb"]=>
  string(0) ""
}*/
?>