And it doesn't really matter -- I don't want you understand why it doesn't have the if statement, but I want you to understand that sometimes you can see a problem in a different way and rewrite it so that a special case goes away and becomes the normal case.
这完全不影响—— 你不必了解这里为什么没有“if”语句， 你需要了解的是 有时候你可以换个角度看问题， 重写代码，排除特例， 完美覆盖所有情况。