17.2 Ensuring consistency 确保一致性

Consistency is hard to maintain, especially when many people work on a project over a long time. People in one group may not know about conventions established in another group. Newcomers don’t know the rules, so they unintentionally violate the conventions and create new conventions that conflict with existing ones. Here are a few tips for establishing and maintaining consistency:

一致性很难维护，尤其是当许多人长时间从事一个项目时。一组人可能不了解另一组中建立的约定。新来者不了解规则，因此他们无意间违反了约定并创建了与现有约定冲突的新约定。以下是建立和保持一致性的一些技巧：

Document. Create a document that lists the most important overall conventions, such as coding style guidelines. Place the document in a spot where developers are likely to see it, such as a conspicuous place on the project Wiki. Encourage new people joining the group to read the document, and encourage existing people to review it every once in a while. Several style guides from various organizations have been published on the Web; consider starting with one of these.

文献。创建一个列出最重要的总体约定的文档，例如编码样式准则。将文档放置在开发人员可能会看到的位置，例如项目 Wiki 上的显眼位置。鼓励新成员加入小组阅读文档，并鼓励现有人员不时审阅该文档。Web 上已经发布了来自各个组织的一些样式指南；考虑从其中之一开始。

For conventions that are more localized, such as invariants, find an appropriate spot in the code to document them. If you don’t write the conventions down, it’s unlikely that other people will follow them.

对于局部性更强的约定，例如不变式，请在代码中找到合适的位置进行记录。如果您不写下约定，那么其他人不太可能会遵循它们。

Enforce. Even with good documentation, it’s hard for developers to remember all of the conventions. The best way to enforce conventions is to write a tool that checks for violations, and make sure that code cannot be committed to the repository unless it passes the checker. Automated checkers work particularly well for low-level syntactic conventions.

执行。即使有好的文档，开发人员也很难记住所有约定。实施约定的最佳方法是编写一个检查违规的工具，并确保除非通过检查程序，否则代码无法提交到存储库。自动检查器对于底层语法约定特别有用。

One of my recent projects had problems with line termination characters. Some developers worked on Unix, where lines are terminated by newlines; others worked on Windows, where lines are normally terminated by a carriage-return followed by a newline. If a developer on one system made a small edit to a file previously edited on the other system, the editor would sometimes replace all of the line terminators with ones appropriate for that system. This gave the appearance that every line of the file had been modified, which made it hard to track the meaningful changes. We established a convention that files should contain newlines only, but it was hard to ensure that every tool used by every developer followed the convention. Every time a new developer joined the project, we would experience a rash of line termination problems while that developer adjusted to the convention.

我最近的一个项目有行终止字符的问题。一些开发人员在 Unix 上工作，行被换行终止;其他的工作在 Windows 上，行通常由一个 carriage-return 后跟一个换行符来结束。如果一个系统上的开发人员对先前在另一个系统上编辑过的文件进行了小的编辑，那么编辑器有时会将所有行终止符替换为适合该系统的行终止符。这给人的感觉是文件的每一行都被修改了，这使得跟踪有意义的更改变得很困难。我们建立了一个约定，即文件应该只包含换行，但是很难确保每个开发人员使用的每个工具都遵循这个约定。每当一个新的开发人员加入这个项目，我们就会经历一连串的线路终止问题，而那个开发人员就会适应这个约定。

We eventually solved this problem by writing a short script that was executed automatically before changes are committed to the source code repository. The script checks all of the files that have been modified and aborts the commit if any of them contain carriage returns. The script can also be run manually to repair damaged files by replacing carriage-return/newline sequences with newlines. This instantly eliminated the problems, and it also helped train new developers.

我们最终通过编写一个简短的脚本解决了这个问题，该脚本在更改提交到源代码存储库之前自动执行。该脚本检查所有已修改的文件，如果其中任何一个包含回车符，则中止提交。还可以通过用换行符替换回车/换行符序列来手动运行脚本以修复损坏的文件。这立即消除了问题，并且还帮助培训了新开发人员。

Code reviews provide another opportunity for enforcing conventions and for educating new developers about the conventions. The more nit-picky that code reviewers are, the more quickly everyone on the team will learn the conventions, and the cleaner the code will be.

代码审查为实施约定和向新开发者提供有关约定的教育提供了另一个机会。代码审阅者越挑剔，团队中的每个人都将更快地学习约定，并且代码越干净。

When in Rome … The most important convention of all is that every developer should follow the old adage “When in Rome, do as the Romans do.” When working in a new file, look around to see how the existing code is structured. Are all public variables and methods declared before private ones? Are the methods in alphabetical order? Do variables use “camel case,” as in firstServerName, or “snake case,” as in first_server_name? When you see anything that looks like it might possibly be a convention, follow it. When making a design decision, ask yourself if it’s likely that a similar decision was made elsewhere in the project; if so, find an existing example and use the same approach in your new code.

在罗马时……最重要的约定是每个开发人员都应遵循古老的格言“在罗马时，就像罗马人一样。” 在处理新文件时，请环顾四周以了解现有代码的结构。是否在私有变量和方法之前声明了所有公共变量和方法？方法是否按字母顺序排列？变量是否使用 firstServerName 中的“ camel case”或使用 first_server_name 中的“ snake case”？当您看到任何看起来可能是约定的内容时，请遵循该约定。在做出设计决策时，请问自己是否有可能在项目的其他地方做出了类似的决策；如果是这样，请找到一个现有示例，并在新代码中使用相同的方法。

Don’t change existing conventions. Resist the urge to “improve” on existing conventions. Having a “better idea” is not a sufficient excuse to introduce inconsistencies. Your new idea may indeed be better, but the value of consistency over inconsistency is almost always greater than the value of one approach over another. Before introducing inconsistent behavior, ask yourself two questions. First, do you have significant new information justifying your approach that wasn’t available when the old convention was established? Second, is the new approach so much better that it is worth taking the time to update all of the old uses? If your organization agrees that the answers to both questions are “yes,” then go ahead and make the upgrade; when you are done, there should be no sign of the old convention. However, you still run the risk that other developers will not know about the new convention, so they may reintroduce the old approach in the future. Overall, reconsidering established conventions is rarely a good use of developer time.

不要更改现有约定。抵制“改善”现有公约的冲动。拥有一个“更好的主意”不足以引起矛盾。您的新想法可能确实更好，但是一致性胜于不一致的价值几乎总是大于一种方法胜过另一种方法的价值。在引入不一致的行为之前，请问自己两个问题。首先，您是否拥有大量的新信息来证明您的方法在建立旧约定时是不可用的？其次，新方法是否好得多，值得花时间更新所有旧用法？如果您的组织同意对两个问题的回答均为“是”，则继续进行升级；否则，请进行升级。完成后，应该没有旧约定的迹象。然而，您仍然冒着其他开发人员不了解新约定的风险，因此他们将来可能会重新引入旧方法。总体而言，重新考虑已建立的约定很少会很好地利用开发人员时间。