What Does It Mean to Refactor Legacy Code? 

Refactoring legacy code involves restructuring the existing codebase without changing its external behavior. It’s about improving the code’s structure and design, making it cleaner, more efficient, and easier to maintain.

Legacy code is often associated with older software, but it can be any code that is difficult to understand, maintain, or extend. It’s the type of code that developers often dread working with because it’s complex, confusing, and usually lacks adequate documentation or tests.

Refactoring legacy code is a critical practice in software development. It’s not just about cleaning up the mess. It’s about turning a liability into an asset, transforming a burden into a reliable foundation for future development.

This is part of a series of articles about Legacy Code

Why Refactor Legacy Code? 

There are several compelling reasons to refactor legacy code. Let’s explore a few of the most important ones.

Improving Maintainability and Readability

One of the main reasons for refactoring legacy code is to improve its maintainability. Legacy code is notoriously difficult to maintain. It’s often written in a convoluted manner, without clear structure or meaningful variable names. By refactoring the code, we can improve its readability, making it easier for developers to understand and work with the code.

Enhancing Performance

Another key reason to refactor legacy code is to enhance its performance. Over time, codebases can become bloated and inefficient, leading to slow execution times and poor user experience. Through refactoring, we can streamline the code, eliminating unnecessary complexity and redundancies, and ultimately improving the software’s performance.

Addressing Security Vulnerabilities

Legacy code often contains security vulnerabilities that can be exploited by malicious actors. These vulnerabilities may be due to outdated programming practices, dependencies on insecure libraries, or simply errors in the code. Refactoring provides an opportunity to review the code and address these vulnerabilities, improving the software’s security.

Facilitating New Features and Integrations

Refactoring legacy code also facilitates future feature additions or integrations. A clean, well-structured codebase is easier to extend and integrate with other systems. It provides a solid foundation for future development, enabling the team to add new features or integrate the software with other systems more efficiently and with fewer risks.

Reducing Long-Term Costs

Finally, refactoring legacy code can reduce long-term costs. While there is an upfront cost associated with refactoring, the long-term savings can be significant. A clean, efficient codebase requires less maintenance, reduces the risk of bugs, and improves team productivity. Over time, these benefits translate into lower costs and higher return on investment.

Refactoring Legacy Code: Pre-Refactoring Steps 

Before you dive into refactoring legacy code, there are a few critical steps you need to take to set yourself up for success.

Understanding the Codebase

The first step in refactoring legacy code is to understand the codebase. This includes understanding the code’s structure, functionality, and dependencies. It’s also crucial to understand the business logic and requirements that the code is intended to fulfill. This understanding will guide your refactoring efforts and help you avoid inadvertently breaking the existing functionality.

Learn more in our detailed guide to legacy codebase (coming soon)

Setting Up a Version Control System

A version control system is a must-have tool for any software development project, and it’s especially important when refactoring legacy code. It allows you to track changes to the codebase, making it easier to identify and rollback changes that cause issues. It also facilitates collaboration, enabling multiple developers to work on the codebase without stepping on each other’s toes.

Creating a Testing Safety Net

Before you start refactoring, you should ensure you have a robust suite of automated tests in place. These tests will help you verify that the refactored code still behaves as expected, preventing regressions. With a robust test suite in place, you can confidently make changes, knowing that if your changes have unexpected side effects, the tests will catch them.

Refactoring Legacy Code: Strategies for Effective Refactoring 

Incremental Changes

Incremental changes mean that instead of rewriting large chunks of code all at once, you should focus on making small, manageable changes one at a time.

This minimizes the risk of introducing new bugs into the system. When you make small changes, it is easier to test that part of the code and ensure that it is working as expected. Furthermore, if you do introduce a bug, it is easier to identify and fix.

Another advantage of making incremental changes is that it allows you to gradually understand the codebase. Legacy code can often be complex and poorly documented. By making small changes, you can slowly build up your understanding of the code, which will make the refactoring process easier in the long run.

Isolating Dependencies

Dependencies are parts of the code that rely on other parts, on third-party libraries, or external  systems to function correctly. If these dependencies are not properly managed, they can create a tangled web of code that is difficult to understand and maintain.

When refactoring, it is important to identify and isolate these dependencies. This can be done by creating interfaces or abstract classes that encapsulate the dependency, making it easier to manage and modify. This also makes the code more modular and easier to test, as you can test each dependency in isolation.

Furthermore, isolating dependencies can make the code more robust and less prone to bugs. If a change is made to one part of the code, it is less likely to affect other parts of the code if the dependencies are well managed.

Prioritizing High-Impact Areas

When refactoring, it can be tempting to try and fix everything at once. However, this is often not feasible or practical. Instead, you should focus on the areas of the code that will have the most impact.

These high-impact areas are typically the parts of the code that are used most frequently, or that are causing the most problems. By focusing your efforts on these areas, you can make the most significant improvements to the codebase.

To identify these high-impact areas, you can use tools like code coverage reports, performance profiling, and bug reports. These tools can help you identify the parts of the code that are used most frequently, or that are causing the most issues.

Using Refactoring Patterns

There are many different refactoring patterns available, each with its own advantages and disadvantages. Some of the most common patterns include Extract Method, Move Method, Rename Method, and Replace Conditional with Polymorphism.

Using refactoring patterns can help to standardize the refactoring process, making it easier to understand and follow. They can also help to improve the quality of the code, by encouraging good coding practices and reducing complexity.

Refactoring Legacy Code: Post-Refactoring Considerations 

Validating Existing Functionality

After you’ve refactored your legacy code, the first post-refactoring consideration is to validate that the functionality remains intact. This means testing the code to ensure that it still works as expected.

This is where unit tests and integration tests come in handy. These tests can help you to verify that the functionality of the code has not been compromised during the refactoring process. If any issues are found, they can be quickly identified and fixed.

Additionally, code reviews can also be a valuable tool for ensuring that the functionality remains intact. By having another developer review your changes, they can provide a fresh perspective and may spot potential issues that you may have overlooked.

Monitoring Performance and Other Metrics

There are many different metrics that you can monitor, including response times, memory usage, and CPU usage. This has two aspects: ensuring the application’s performance has not deteriorated as a result of refactoring, and measuring the success of refactoring in improving performance. By comparing the performance of the application before and after the refactoring, you can determine whether the changes have had a positive or negative impact.

Gathering Feedback from End-Users or Stakeholders

Gathering feedback from end-users or stakeholders can provide valuable insights into how the refactoring has impacted the user experience.

Feedback can be gathered through surveys, interviews, or user testing sessions. This feedback can help you to identify any issues that may have arisen as a result of the refactoring, or any areas that could be improved further.

Legacy Code Documentation with Swimm

Refactoring legacy code is a practice that goes beyond merely tidying up messy code; it’s about turning the burden of legacy code into a solid foundation for future development. Refactoring paves the way for improved maintainability, enhanced performance, security fortification, and the seamless integration of new features. The long-term benefits in reduced costs and increased productivity make it a strategic investment for any organization.

Swimm is a dev tool designed to make legacy code documentation easier and more accessible. In essence, it makes the entire refactoring process easier. Swimm’s code-coupled documentation, combined with its easy discoverability in the IDE, makes it an ideal companion for your refactoring efforts. With Swimm, you can ensure that your documentation remains up to date as your code changes, improving your team’s productivity and code quality.

Learn more about Swimm