What are some common causes and solutions for duplicated code?

1 Why does duplicated code happen?

Duplicated code can occur for a variety of reasons, including copying and pasting code from one source to another without changing it, implementing the same or similar functionality in different classes or modules without using inheritance, abstraction, or composition, writing code that is too specific or hard-coded for a particular case, and not following the DRY (Don't Repeat Yourself) principle. This principle states that every piece of knowledge or logic should have a single, unambiguous, and authoritative representation in the code.

2 How to detect duplicated code?

Duplicated code can be detected by utilizing a variety of tools and techniques, such as code analysis tools like PMD, SonarQube, Code Climate, and Codacy. Additionally, code review tools like GitHub, GitLab, Bitbucket, and Gerrit can be used to compare and comment on different versions or branches of your code. To further identify and remove duplicated code during the code review process, checklists, guidelines, and standards should be employed.

3 How to fix duplicated code?

Duplicated code can be fixed by applying various refactoring techniques, such as extracting common code into methods, functions, or classes that can be reused in different places; using inheritance, abstraction, or composition to create hierarchies or relationships between classes or modules with similar functionality; and replacing hard-coded values or expressions with parameters, variables, constants, or enums that can be configured or changed easily. These techniques reduce duplication and improve cohesion, modularity, flexibility, and readability while avoiding magic numbers or strings.

5 How to improve your code review skills?

Code review is a valuable skill that can help you identify and fix duplicated code, as well as other code smells and issues. To improve your code review skills, you can learn from other developers and reviewers by reading their code, comments, and feedback. You can also use code review tools and platforms that provide features like diff view, annotations, comments, suggestions, approvals, and merge requests. Additionally, it is important to follow code review best practices and guidelines that ensure a constructive, respectful, and collaborative code review culture. Checklists, templates, or rubrics can also be used to guide your code review process and criteria.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?