构和类又非常多的相似之处，如结构可以实现界面，和可以拥有和类一样的成员。结构与类也有一些重要的区别：结构是值类型，而不是引-conformation and category there are many similarities, such as the interface structure can be achieved, and can have and the members of the same category. The class structure are some impo