Legacy Codebase: All you Need to Know

You could’ve heard about the mysterious legacy codebase, written long ago and forgotten. In colloquial terms, it’s about “the code developers wrote who are no longer in the company and no one knows how to work with it.” That’s why it’s “legacy”, it was inherited from the previous teams or even companies. However, there’s much more to the term. And I’ll try to describe the concept and my experience working effectively with legacy code.

What is Legacy Code?

The definition is due. Legacy codebase refers to software systems or applications that were developed using outdated technology and programming practices. That’s one way to look at it: apps that were built on old-fashioned methods. Also, the more accurate definition might be:

“Legacy code refers to code that has been inherited from previous developers or software systems and is no longer actively maintained or supported. This type of code can be difficult to work with because it may not have documentation, use outdated programming languages or frameworks, and not adhere to current coding standards.”

There are even more answers to “what is legacy code?” and they are rather different. The heated discussions on Stackoverflow are proof of that.

Based on these definitions, the main characteristics of such code are:

• relatively old codebase still in use
• lacks documentation (or has quite poor one)
• original author(s) can’t be found
• lacks tests or type system
• doesn’t follow modern practices (has no context in code)
• uses technologies that are mostly not in use (hard to find specialists)

All those factors make the legacy codebase hard to work with. Like an onion with many layers that sting when you peel them. Ivo Lukač in his survey claimed that half of dev respondents would rather not work on legacy code, and 11% simply hate it. As the old wisdom says: “We shouldn’t touch that. It’s legacy code.”

How to Improve and Reduce Legacy Code?

Working effectively with old code requires analysis, costs, and developer dedication. I can’t underestimate the patience it takes to get to the bottom of the issue, refactor and rebuild the system. Techniques on how to work with legacy codebases are structuring the work and helping clarify the steps.

The most valuable advice I found out is refactoring code and providing context to your code. We’ll get to refactoring soon but the second piece of advice is even more vital. It’s often harder to read code than to write it. So, giving context is the least you could do for the next teams of developers. Improving code quality is important and commenting on code is even more vital for readability. The documentation is a necessary step as well as setting up the environment in the code editor.

Stepsize VS Code and any JetBrains extension help teams gain actionable insights into technical debt. Legacy code is usually a part of tech debt. In these extensions, devs can track debt, add bookmarks, and organize their tasks in the code editor.

Refactoring: a Miracle Pill for Codebase

Don’t trust the heading (it’s got a twist to it). Refactoring code can do miracles when done gradually and with backup versions. The full definition of refactoring by Martin Fowler:

"Refactoring is the process of changing a software system in such a way that it does not alter the external behavior of the code yet improves its internal structure. It is a disciplined way to clean up code that minimizes the chances of introducing bugs. In essence, when you refactor you are improving the design of the code after it has been written.”

The idea is to change a piece of code, then a few more, and gradually improve the overall system. With the legacy code base, it’s the same. Any unnecessary lines of code should be removed or rewritten. Classes and variables are simplified and merged. Command methods are rewritten. The code we get is easier to read, maintain, and adapt.

Take a look at the code snippets:

Before the refactoring:

After refactoring:

Refactoring legacy code is by far the most effective way to gradually get systems going. However, you need to understand the code before improving and test after changing.

More Ways

Actually, it’s one way: Active maintenance and testing. When you leave any code unattended, it isn’t stable. The features become outdated, the third-party integrations stop working, and everything gets slow. You get the idea. So, we need to have some time to maintain the code, fix the broken parts, and test. To do that, we need:

• Actively deprecate and remove code that no longer serves a purpose.
• Track evolving language standards and libraries.
• Fix the bugs and check for vulnerabilities.
• Get the app up to security standards and do penetration testing.
• go through different software testing levels (especially unit tests) once in a while

Sum Up

Working effectively with legacy code is no easy task.  Some software developers sometimes use the languages to maintain legacy systems. However, this approach gets too costly and resource-draining. The two courses of action would be to rewrite the system entirely or refactor it until it works better. In the first case, it’s an entirely new project with significant costs and no guarantee you’ll do better this time. The second is cost-effective but it’s time-consuming and risky too. My opinion is: Legacy code bases that have business value should be improved gradually. What do you think?