创建模板类（封装一个类）
新建一个名字叫做 Product 的类

Product.swift File 的内容

class Product {
    var name: String
    var description: String
    var price: Double
    var stock: Int
    init(name: String, description: String, price: Double, stock: Int) {
        self.name = name
        self.description = description
        self.price = price
        self.stock = stock
    }
}

Swift:简单封装一个工具类模板