Code Duplication

Owned by Shir Koretski
Dec 20, 2024
3 min read

Revealing Code Reusability

Overview
Code duplication, particularly through copy-pasting, can significantly hinder the maintainability and readability of a codebase. Reducing unnecessary duplication is a key indicator of high-quality code, as it makes future updates more efficient and improves overall code comprehension.

What Does This Metric Measure?

This metric tracks the amount of duplicated code within a codebase by measuring code similarity in commits. High duplication often means that the code is harder to maintain, more error-prone, and more difficult to update as requirements evolve.

How Is This Metric Calculated?

The metric is calculated by evaluating code similarity within the lines added in a commit. The score reflects the extent to which the added lines are duplicated:

  • Score of 100: Indicates that multiple copies of the same line of code have been added in the commit (i.e., heavy duplication).

  • Score of 0: Means all added lines are unique with no duplications.

Note: This metric only considers added lines of code and does not factor in removed or modified lines.

What Questions Can I Answer from This Data?

This metric helps you answer key questions about code duplication and reusability:

  1. Are developers copying and pasting a large amount of code?
    You can see whether there is significant duplication in the codebase, which can point to areas where code reuse could be improved.

  2. Can we identify patterns or trends in the code similarity metric over time or across different commits?
    Track whether duplication is increasing or decreasing over time, helping you understand if the team is improving code quality or if issues are worsening.

  3. How can we interpret the scores between 0-100 in terms of code similarity within commits?
    A score closer to 100 indicates significant duplication, while a score closer to 0 indicates more original or unique code. This gives you a quick snapshot of how "reused" the code is within a commit.

What Should I Take Away from This Data?

  1. Minimize Code Duplication
    Highly duplicative codebases are difficult to maintain and are often a source of bugs or defects in the long term. Reducing duplication can help make the codebase more flexible, easier to test, and simpler to update.

  2. Addressing Significant Duplication
    When significant code duplication is detected, it’s important to understand why it's happening. Is it due to a lack of reusable functions, poor architecture, or simply developers copying and pasting code?

    A thorough review is essential to determine whether refactoring or reusing existing code would be more efficient than adding new duplicated lines.

  3. Engage with Developers
    If new duplications are being added, it's a good practice to talk to the developers involved. Encourage discussions on how to avoid duplication, such as creating reusable functions, modules, or adopting design patterns like DRY (Don't Repeat Yourself).

  4. Long-Term Code Health
    Focusing on minimizing duplication will help improve long-term code health, reduce technical debt, and improve the speed at which future development work can be done.

Conclusion

The Code Reusability Metric is a vital tool for ensuring that your codebase remains clean, maintainable, and scalable. By monitoring duplication levels, identifying patterns, and addressing excessive copy-paste practices, teams can improve the quality of the codebase and reduce the risk of introducing defects.