购物车类实现

class cart {    static protected $ins = null;    protected $basket = array();        protected function __construct() {    }    static protected function getIns() {        if(self::$ins == null) {            self::$ins = new self();        }        return self::$ins;    }    static public function getCart() {        // 如果session['cart']不存在,或者存在但不是cart类的实例        if(!isset($_SESSION['cart']) || !($_SESSION['cart'] instanceof self)) {            $_SESSION['cart'] = self::getIns();        }        return $_SESSION['cart'];    }    // 添加商品到购物车    // 有商品名称,商品id,商品本店价格,购买数量    public function addItem($id,$name,$shop_price,$num) {        if(!$this->hasItem($id)) {            $this->basket[$id] = array('name'=>$name,'shop_price'=>$shop_price,'num'=>$num);        } else {            $this->basket[$id]['num'] += $num;        }    }    // 删除商品    public function delItem($id) {        if($this->hasItem($id)) {            unset($this->basket[$id]);        }    }    // 判断某商品是否存在    public function hasItem($id) {        return array_key_exists($id,$this->basket);    }    // 修改商品数量    public function modItem($id,$num) {        if($num == 0) {            $this->delItem($id);            return;        }        if($this->hasItem($id)) {            $this->basket[$id]['num'] = $num;        }    }    // 商品加1    public function incItem($id) {        if($this->hasItem($id)) {            $this->basket[$id]['num'] += 1;        }    }    // 商品-1    public function decItem() {        if($this->hasItem($id)) {            $this->basket[$id]['num'] -= 1;        }                // 要是减到0了,则删掉        if($this->basket[$id]['num'] == 0) {            $this->delItem($id);        }    }    // 计算商品种类    public function cnt() {        return count($this->basket);    }        // 返回商品列表    public function items() {        return $this->basket;    }    // 计算商品的个数    public function getCount() {        if($this->cnt() == 0) {            return 0;        }        $count = 0;        foreach($this->basket as $v) {            $count += $v['num'];        }        return $count;    }    // 计算商品的总价格    public function getPrice() {        if($this->cnt() == 0) {            return 0;        }        $price = 0;        foreach($this->basket as $v) {            $price += $v['num'] * $v['shop_price'];        }        return $price;    }    // 清空购物车    public function clear() {        $this->basket = array();    }}