function doSomething($actionStr, ...$args){
    $actionArr = str_split($actionStr);

    foreach($args as $i => $n) {

        switch ($actionArr[$i]) {
            case 'd':
                echo "Decimal: " . $n . '<br>';
                break;
            case 's':
                echo "String: " . $n . '<br>';
                break;
            default:
                break;
        }
    }
}

// ------------- CASE 1 ---------------------------
// In this case I have 5 arguments. So I can do this:
$a = 10;
$b = 20;
$c = 'hello';
$d = 'cheese';
$e = 500;

if($a && $b && $c && $d && $e){
    doSomething('ddssd', $a, $b, $c, $d, $e);
}

/* OUTPUT:
Decimal: 10
Decimal: 20
String: hello
String: cheese
Decimal: 500
 */

echo '<hr>';

// ------------- CASE 2 ---------------------------
// I'm using 4 variables

$e = null;

if($a && $b && $c && $d && !$e){
    doSomething('ddss', $a, $b, $c, $d);
}

/* OUTPUT:
Decimal: 10
Decimal: 20
String: hello
String: cheese
 */

echo '<hr>';
// ------------- CASE 3 ---------------------------
// 3 variables
$d = null;
$e = null;

if($a && $b && $c && !$d && !$e){
    doSomething('dds', $a, $b, $c);
}

/* OUTPUT:
Decimal: 10
Decimal: 20
String: hello  */

echo '<hr>';

// ------------- CASE 4 ---------------------------
// I want to have a more generic approach.

$argumentList = array(
    'a' => 10,
    'b' => 20,
    'c' => null,
    'd' => null,
    'e' => null,
);
$argumentList = array_filter($argumentList);

$actionStr = '';
foreach($argumentList as $k => $v){

    if(is_numeric($v)){
        $actionStr .= 'd';
    }

    if(is_string($v)){
        $actionStr .= 's';
    }
}

$varList = array_values($argumentList);
$param_arr = array();
$param_arr[] = $actionStr;
$param_arr = (array_merge($param_arr, $varList));
call_user_func_array('doSomething', $param_arr);

/* OUTPUT:
Decimal: 10
Decimal: 20  */