PHP use闭包函数

<?php

class Cart 

{ 

//产品价格

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) 

{ 

// echo __CLASS__ ."::PRICE_" . strtoupper($product);die;

$pricePerItem = constant(__CLASS__ ."::PRICE_" . strtoupper($product)); 

// echo $pricePerItem.'<br>';

$total += ($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); 

// 打出出总价格，其中有 5% 的销售税. 

print $my_cart->getTotal(0.05) . " "; 

// The result is 54.29 

?>