其提供一个用于套接字绑定、连接或作为返回值的不变对象。
It provides an immutable object used by sockets for binding, connecting, or as returned values.
每个都可以赋值给一个变量，作为参数传递，或作为返回值从函数中返回。
Each can be assigned to a variable, passed as an argument, or returned from a function. For instance, here's an example of storing a function.
不要使用定制类型作为参数或返回值。
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