Change, Similarity and Redundancy in Software

软件克隆被定义为软件系统中的重复或类似的代码片段。复制代码片段并通过粘贴编辑更改来重用它是软件开发中的一种常见做法。事实上，开发人员经常故意使用克隆，因为克隆具有潜在的好处，例如更快的开发速度、通过避免风险来重用经过良好测试的代码，或者分配给他们的时间限制。另一方面，在Flower的重构列表中，克隆是排名第一的代码“臭味”。最近对工业软件和开源软件的研究表明，虽然克隆并不总是有害的，克隆在许多方面都是有用的，但其中许多克隆也可能对软件维护不利。当然，重用包含未知错误的片段可能会导致错误传播，或者克隆片段中的任何更改都可能导致对其所有类似片段的更改，这具有挑战性、耗时且容易出错。因此，克隆被认为是软件高维护成本的主要贡献者之一，软件维护成本高达总开发成本的80%。

Software clones are defined to be duplicated or similar fragments of code in a software system. Copying a code fragment and reusing it by pasting with editing changes is a common practice in software development. Developers in fact often intentionally practice cloning because of the underlying benefits such as faster development, reuse of well-tested code by avoiding risks, or time limits assigned to them. On the other hand, clones are the #1 code “bad smell” in Flower’s refactoring list. Recent studies both with industrial and open source software show that while clones are not always harmful and clones can be useful in many ways, many of them can also be detrimental to software maintenance. Of course, reusing a fragment containing unknown bugs may result in fault propagation, or any changes in a cloned fragment may lead to changes to all the similar fragments to it, which is challenging, time consuming, and error-prone. Clones are thus considered to be one of the primary contributors to the high maintenance cost of software, which is up to 80% of the total development cost.