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Closures may also inherit variables from the parent scope. Any such variables must be declared in the function header. Inheriting variables from the parent scope is not the same as using global variables. Global variables exist in the global scope, which is the same no matter what function is executing. The parent scope of a closure is the function in which the closure was declared (not necessarily the function it was called from). See the example below:


// A basic shopping cart which contains a list of added products
// and the quantity of each product. Includes a method which
// calculates the total price of the items in the cart using a
// closure as a callback.

class Cart
    const PRICE_BUTTER  = 1.00;
    const PRICE_MILK    = 3.00;
    const PRICE_EGGS    = 6.95;

    protected $products = array();

    public function add($product, $quantity)
        $this->products[$product] = $quantity;

    public function getQuantity($product)
        return isset($this->products[$product]) ? $this->products[$product] :

    public function getTotal($tax)
        $total = 0.00;

        $callback =
            function ($quantity, $product) use ($tax, &$total)
                $pricePerItem = constant(__CLASS__ . "::PRICE_" .
                $total += ($pricePerItem * $quantity) * ($tax + 1.0);

        array_walk($this->products, $callback);
        return round($total, 2);

$my_cart = new Cart;

// Add some items to the cart
$my_cart->add('butter', 1);
$my_cart->add('milk', 3);
$my_cart->add('eggs', 6);

// Print the total with a 5% sales tax.
print $my_cart->getTotal(0.05) . "\n";
// The result is 54.29