class Handler
{
    public function getHandler()
    {
        return 'some handler';
    }

    public function getFile()
    {
        return 'some file';

}
}

$handler = $class->getHandler();
$file    = $class->getFile();

public function getHandler() {
    // {
    // ...
    // возможно блок каких-либо действий
    // ...
    // }
    return $this;
}

class TestClass {
    public static $currentValue;

    private static $_instance = null;

    private function __construct() { }

    public static function getInstance() {
        if (self::$_instance === null) {
            self::$_instance = new self;
        }

        return self::$_instance;
    }

    public function toValue($value) {
        self::$currentValue = $value;
        return $this;
    }

    public function add($value) {
        self::$currentValue = self::$currentValue + $value;
        return $this;
    }

    public function subtract($value) {
        self::$currentValue = self::$currentValue - $value;
        return $this;
    }

    public function result() {
        return self::$currentValue;
    }
}

$result = TestClass::getInstance()
    ->toValue(5)
    ->add(3)
    ->subtract(2)
    ->add(8)
    ->result();

echo $result; // выведет 14

$file = $$handler->getFile();

$function_name = 'getHandler';
$result = $file->{$function_name}();