So you're implementing this black box, and if its purpose in life is to actually return a value, you have to tell the compiler what kind of value to expect, and this is going to have ripple effects.

你在实现这个黑盒子，如果它的目的是,返回一个值，你必须告诉编译器你期望的是什么类型的值，这个将是一个连锁反应。

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And again, a related problem that people run into is side-effects. You call a function and it returns a value, but maybe it, on purpose or on accident, modifies one of the actual parameters.

另外，一个人们常碰到的相关问题,就是副作用，你调用一个函数它返回一个值,但是故意或者无意的,它可能会修改一个实参的值。

麻省理工公开课 - 计算机科学及编程导论课程节选