想象一下可以修改子程序的返回值！
Imagine being able to modify the return value of your subroutine!
第一个子程序 socket_setup() ，它返回一个准备接受连接的套接字。
The first one, socket_setup(), returns a socket which is ready to accept connections.
第一个子程序 socket_setup() ，它返回一个准备接受连接的套接字。
The first one, socket_setup(), returns a socket which is ready to accept connections.
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