9.3 Bring together to eliminate duplication 消除重复

If you find the same pattern of code repeated over and over, see if you can reorganize the code to eliminate the repetition. One approach is to factor the repeated code out into a separate method and replace the repeated code snippets with calls to the method. This approach is most effective if the repeated code snippet is long and the replacement method has a simple signature. If the snippet is only one or two lines long, there may not be much benefit in replacing it with a method call. If the snippet interacts in complex ways with its environment (such as by accessing numerous local variables), then the replacement method might require a complex signature (such as many pass-by-reference arguments), which would reduce its value.

如果发现反复重复相同的代码模式，请查看是否可以重新组织代码以消除重复。一种方法是将重复的代码分解为一个单独的方法，并用对该方法的调用替换重复的代码段。如果重复的代码段很长并且替换方法具有简单的签名，则此方法最有效。如果代码段只有一两行，那么用方法调用替换它可能不会有太多好处。如果代码段与其环境以复杂的方式进行交互（例如，通过访问多个局部变量），则替换方法可能需要复杂的签名（例如，许多“按引用传递”参数），这会降低其价值。

Another way to eliminate duplication is to refactor the code so that the snippet in question only needs to be executed in one place. Suppose you are writing a method that needs to return errors at several different points, and the same cleanup actions need to be performed at each of these points before returning (see Figure 9.1 for an example). If the programming language supports goto, you can move the cleanup code to the very end of the method and then goto that snippet at each of the points where an error return is required, as in Figure 9.2. Goto statements are generally considered a bad idea, and they can result in indecipherable code if used indiscriminately, but they are useful in situations like this where they are used to escape from nested code.

消除重复的另一种方法是重构代码，使相关代码段仅需要在一个地方执行。假设您正在编写一种方法，该方法需要在几个不同的点返回错误，并且在返回之前需要在每个这些点执行相同的清除操作（示例请参见图 9.1）。如果编程语言支持 goto，则可以将清除代码移到方法的最后，然后在需要返回错误的每个点处转到该片段，如图 9.2 所示。Goto 语句通常被认为是一个坏主意，如果不加选择地使用它们，可能会导致无法识别的代码，但是在诸如此类的情况下，它们可用于从嵌套代码中转义，因此它们非常有用。