三次法则¶

名称: 三次法则 The Rule of Three

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　　Don Roberts 给了我一条准则：第一次做某件事时只管去做；第二次做类似的事会产生反感，但无论如何还是做了；第三次再做类似的事，你就应该重构。事不过三，三则重构。（Three strikes and you refactor）——《重构：改善既有代码的设计》

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It states that you are allowed to copy and paste the code once, but that when the same code is replicated three times, it should be extracted into a new procedure. The rule was introduced by Martin Fowler in his text “Refactoring” and attributed to Don Roberts.