Places in code with 6 or more lines that are exactly the same.
- For duplication, we look at places in code where there are 6 or more lines of code that are exactly the same.
- Before duplication is calculated, the code is cleaned to remove empty lines, comments, and frequently duplicated constructs such as imports.
- You should aim at having as little as possible (<5%) of duplicated code as high-level of duplication can lead to maintenance difficulties, poor factoring, and logical contradictions.
Learn more...
- To learn more about duplications and techniques for eliminating duplication, Sokrates recommends the following resources:
- Avoid Repetition, MartinFlower.com (IEEE Software article)
- Refactoring duplicated code, sourcemaking.com
- Beck Design Rules, MartinFowler.com
- DRY (Don't Repeat Yourself) Principle, Wikipedia
- The Cut-and-Paste Programming Software Development Anti-Pattern, sourcemaking.com
- Code Smells / Duplicated Code, Jeff Atwood, codinghorror.com:
- "Duplicated code is the bane of software development. Stamp out duplication whenever possible. You should always be on the lookout for more subtle cases of near-duplication, too. Don't Repeat Yourself!"
- Reducing Coupling, MartinFlower.com (IEEE Software article):
- "There are several ways to describe coupling, but it boils down to this: If changing one module in a program requires changing another module, then coupling exists. ... Duplication always implies coupling, because changing one piece of duplicate code implies changing the other."
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