Abstract
Clones are generally considered bad programming practice in software engineering folklore. They are identified as a bad smell (Fowler et al. 1999) and a major contributor to project maintenance difficulties. Clones inherently cause code bloat, thus increasing project size and maintenance costs. In this work, we try to validate the conventional wisdom empirically to see whether cloning makes code more defect prone. This paper analyses the relationship between cloning and defect proneness. For the four medium to large open source projects that we studied, we find that, first, the great majority of bugs are not significantly associated with clones. Second, we find that clones may be less defect prone than non-cloned code. Third, we find little evidence that clones with more copies are actually more error prone. Fourth, we find little evidence to support the claim that clone groups that span more than one file or directory are more defect prone than collocated clones. Finally, we find that developers do not need to put a disproportionately higher effort to fix clone dense bugs. Our findings do not support the claim that clones are really a “bad smell” (Fowler et al. 1999). Perhaps we can clone, and breathe easily, at the same time.
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Acknowledgements
We would like to thank Adrian Bachmann and Avi Bernstein for the Univ. of Zurich bug linking data. We also thank Lingxiao Jiang, Ghassan Mishergi, Zhendong Su and Stephane Glondu for providing us DECKARD. We extend our gratitude to anonymous reviewers for valuable comments on this paper. We acknowledge support from an IBM Faculty Fellowship, and a gift from Microsoft Research. Most of all we acknowledge with gratitude support from the NSF Science of Design Program, grant No. SoD-TEAM 0613949. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.
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Editors: Jim Whitehead and Tom Zimmermann
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Rahman, F., Bird, C. & Devanbu, P. Clones: what is that smell?. Empir Software Eng 17, 503–530 (2012). https://doi.org/10.1007/s10664-011-9195-3
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DOI: https://doi.org/10.1007/s10664-011-9195-3