第 13 章 注释应该描述代码中不明显的内容

The reason for writing comments is that statements in a programming language can’t capture all of the important information that was in the mind of the developer when the code was written. Comments record this information so that developers who come along later can easily understand and modify the code. The guiding principle for comments is that comments should describe things that aren’t obvious from the code.

One of the most important reasons for comments is abstractions, which include a lot of information that isn’t obvious from the code. The idea of an abstraction is to provide a simple way of thinking about something, but code is so detailed that it can be hard to see the abstraction just from reading the code. Comments can provide a simpler, higher-level view (“after this method is invoked, network traffic will be limited to maxBandwidth bytes per second”). Even if this information can be deduced by reading the code, we don’t want to force users of a module to do that: reading the code is time-consuming and forces them to consider a lot of information that isn’t needed to use the module. Developers should be able to understand the abstraction provided by a module without reading any code other than its externally visible declarations. The only way to do this is by supplementing the declarations with comments.

This chapter discusses what information needs to be described in comments and how to write good comments. As you will see, good comments typically explain things at a different level of detail than the code, which is more detailed in some situations and less detailed (more abstract) in others.