Can you explain the difference between assigning references in PHP, and how it affects the behavior of variables within classes and global scope?

Assigning references in PHP allows variables to refer to the same underlying data, meaning changes to one variable will affect the other. This can be useful for avoiding unnecessary copying of large data structures. When assigning references within classes, changes to the reference variable will affect all instances of the class, while in the global scope, changes to the reference variable will affect all references to that variable.

// Assigning references within a class
class MyClass {
    public $data;
    
    public function __construct(&$data) {
        $this->data = &$data;
    }
}

$data = 10;
$obj1 = new MyClass($data);
$obj2 = new MyClass($data);

$obj1->data = 20;
echo $data; // Outputs 20

// Assigning references in global scope
$data = 10;
$ref = &$data;

$ref = 20;
echo $data; // Outputs 20