PHP工厂模式

class yunsuan
{
    public $a;
    public $b;
    function suan()
    {
     echo "对两个数进行运算";
    }
}
class jia extends yunsuan
{
    function suan()
    {
        return $this->a+$this->b;
    }
}
class jian extends yunsuan
{
    function suan()
    {
        return $this->a-$this->b;
    }
}
class cheng extends yunsuan
{
    function suan()
    {
        return $this->a*$this->b;
    }
}
class chu extends yunsuan
{
    function suan()
    {
        return $this->a/$this->b;
    }
}
//对扩展开放，对修改封闭
//工厂类
class gongchang
{
    //给一个参数，返回一个对象
    static function chanpin($name)
    {
        switch ($name)
        {
            case"+":
                return new jia();
                break;
            case"-":
                return new jian();
                break;
            case"*":
                return new cheng();
                break;
            case"/":
                return new chu();
                break;
        }
    }
}
//$a=gongchang::chanpin("+");
//var_dump($a);
//$a=gongchang::chanpin("-");
//var_dump($a);
//$a=gongchang::chanpin("*");
//var_dump($a);
$a=gongchang::chanpin("/");
var_dump($a);