The source code is the same for both the master and the receiver, with the functionality being decided using the rank that the world object provides (see Listing 16.
主进程和接收者进程的源代码是相同的，使用 world 对象提供的等级决定功能（见 清单 16）。
2
Because it's easy to lift up the receiver and say, "Hello!" and it's magical to hear an answer, this is one of their first opportunities to master a grown-up task.