PHP 购物车 php闭包 array_walk

<?php
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] :
FALSE;
}

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

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

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

$my_cart = new Cart;

// 往购物车里添加条目
$my_cart->add('butter', 1);
$my_cart->add('milk', 3);
$my_cart->add('eggs', 6);

print $my_cart->getQuantity('milk');
echo "<br/>";
// 打出出总价格，其中有 5% 的销售税.
print $my_cart->getTotal(0.05) . "\n";
// 最后结果是 54.29
?>