protected static function swap(&$a, &$b, &$flipped)
    {
        $c = $a;
        $a = $b;
        $b = $c;
        $flipped = !$flipped;
    }
protected static function swap(&$a, &$b, &$flipped)
    {
        $c = $a;
        $a = $b;
        $b = $c;
        $flipped = !$flipped;
    }
protected static function swap ( & $ a , & $ b , & $ flipped ) { $ c = $ a ; $ a = $ b ; $ b = $ c ; $ flipped = ! $ flipped ; }
Swaps two variables.

@param mixed $a
The first variable which will become the second.
@param mixed $b
The second variable which will become the first.
@param bool $flipped
The boolean indicator which will change its value.
Swaps two variables .