最佳实践在函数/类中使用全局变量或通过引用函数传递变量？

What’s the best practice with PHP 5.6+? What is the more sparing method? Relating to resources / memory / speed.

Pass a variable by reference to a function. I don’t need to modify the variable:

$bigClass = new MyBigClass();

class MyClass extends AnotherClass
{
    protected $obj;

    function __construct(
amespace\interface &$obj) {
        $this->obj =& $obj;
    }

    public function function1() {
        $this->obj->doThings();
    }

    private function function2() {
        $this->obj->otherThings();
    }

    public function function3() {
        // and so on ...
    }
}

$my_class = new MyClass($bigClass);
// $my_class->...

or should I use the way with the global Keyword:

$bigClass = new MyBigClass();

class MyClass extends AnotherClass
{
    function __construct() { }

    public function function1() {
        global $bigClass;
        $bigClass->doThings();
    }

    private function function2() {
        global $bigClass;
        $bigClass->otherThings();
    }

    public function function3() {
        // and so on ...
    }
}

$my_class = new MyClass();
// $my_class->...

Which method consumes the most resources and is slow?

Or to be nothing to speak of?

Thanks