当你想将函数的返回引用绑定到某个变量时，PHP允许你这么做：

function &returns_reference()
{
    static $someref = 0;
    $someref++;
    return $someref;
}

$newref = &returns_reference();//引用返回,相当于 $newref = &$someref;
echo $newref; //1

$notref = returns_reference(); //值传递的是副本
$newref = 100;
echo $notref; //2

$newref = 100;
echo returns_reference(); //101

可见，想让函数返回引用，必须在函数申明和赋值时都带上&操作符。 
对于类中方法也是如此：

class foo {
    public $value = 0;

    public function &getValue() {
        return $this->value;
    }
}

$obj = new foo;
$myValue = &$obj->getValue(); // $myValue is a reference to $obj->value, which is 42.
$obj->value = 2;
echo $myValue;