What is Legacy Code? How to Use Modern Solutions to Fix Ancient Coding Problems

Sooner or later, you’re going to encounter legacy code. But with testing and today’s software solutions, you can create a new, cleaner legacy for your project and your business. 

What Is Legacy Code?

A large part of software development is keeping up to date with the latest coding and software development practices. And while these updates often result in faster, better, and more maintainable software, one side effect can often be legacy code.

Legacy code can sometimes be a challenge for even more advanced software developers, and today the answer to the question, what is legacy code, can have many different answers. Oftentimes, legacy code refers to source code that is no longer supported or code which is derived from an older version of the software. It can also be any code that you may have inherited from the original developer. It can also be code that is simply difficult to understand or change. Other programmers have even taken the approach that code becomes legacy code immediately — as soon as it is created– essentially, making all code legacy code.   

Michael Feathers’ popular answer to the what is legacy code question is that legacy code is “code without tests“. This helps to illustrate the idea that legacy code is difficult to work with, in part, due to the lack of testing. 

Whatever definition of legacy code you use, unless you are starting a brand new project, it is going to pop up. But analyzing, maintaining, and fixing legacy code as needed can help you to maintain clean code and create a piece of software that can last for the necessary period of time.

Why is Legacy Code Such a Challenge?

Legacy code can be a challenge for several reasons. Legacy software and legacy code bases may be written in an unfamiliar programming language. A piece of code may be bulky and incompatible with your more modern software. It could be especially lengthy. But, many times, the biggest challenge of legacy code is simply the developer’s approach to it. It may be written off as bad code or “spaghetti code.” It might have been poorly documented. Perhaps the developer thinks he could write it better. Whether this is true or not, usually the code has been written in a certain way for a reason, even if that reason is unknown to us at the time. But, by thinking in this manner, we can look beyond the perceived lines of code and instead start to think about why it might have been written this way. There may be possible dependencies that we don’t yet know about. 

But legacy code is not just a challenge for programmers. It can also be very costly to your business. Aging systems can be notoriously expensive to maintain as new software evolves and older software is phased out. What’s more, achieving today’s required compliance levels is also difficult, costly, and time-consuming for legacy code bases. And as time goes on, legacy code only becomes more expensive as developers with the required skill sets become more difficult to find. You may have to spend a lot of time (and money) finding the right person or re-training one of your current developers. Often, this legacy code is less efficient than modern code, further driving up costs. It is also possible that the legacy code is not even compatible with modern solutions, further adding to the difficulty and expense of legacy systems. 

How to Manage Your Legacy Code

After you have answered the question of what is legacy code, you will then need to manage your legacy code. Almost every software project will have at least one legacy code base that programmers will try to avoid, but avoiding the code base is not going to make it any more manageable. Instead, there are a few approaches for programming and managing the code that can be utilized to help control the legacy code. 

First, test the code. And when it comes to testing and handling legacy code, the first book for software developers and programmers to reach for is Working Effectively with Legacy Code by Michael Feathers. Feathers takes a pragmatic look at fixing broken software and cleaning up bad legacy code through testing and incremental refactoring. This book may help with refactoring techniques and actual refactoring steps that can help you to create clean, well-modelled code.

Refactoring allows you to alter the structure of the code, without changing its functionality. This, in turn, acts as a type of code cleaner, eliminating potential errors while also making it easier to understand and helping to eliminate potential errors.

When refactoring code, it’s best to start with the easiest part of the code that you have and work your way from there. Often, this is your deepest code point. After refactoring, test to ensure that everything is still working properly. Also be sure to have a safety net in place, something like continuous integration, so that you can always go back to your previous build if needed. And always refactor legacy code that has unit tests. This way you can be sure to know what you have. Refactoring code is often better than rewriting it. Rewriting legacy code bases can take too much of your time and resources, while also potentially introducing new bugs and removing needed functionality.

Additionally, you can take advantage of a code quality tool or code analysis tool that can help identify potential code problems and can also support you with a better understanding of how exactly your legacy code functions. 

As you are updating and refactoring the code, do not make too many changes at one time, such as refactoring and making functional changes in the same cycle. This can make it difficult when it comes time for your code review. Instead, keep your changes more isolated. 

It may also be helpful for you to work together with other developers who might have a better working knowledge of the code base. It never hurts to consult with co-workers that you can trust, and, through collaboration, you may encounter potential problems or solutions that one developer alone can often miss. Along those lines, be sure to review any documentation that you may have access to. This will not only give you a better understanding of the code itself, but it can also help you to keep improving the code without compromising any of the system’s integrity. 

Once you have your new code, keep it clean! You don’t want to pass on bad legacy code to someone else or introduce new problems. Keep clean code and clean architecture by sticking to best practices and you’ll be more likely to achieve bug-free code and higher software quality all around. 

How Sider can Help Fix Legacy Code

No matter where you go as a software developer, you are going to find legacy code. It may have resulted as a matter of business goals or business logic. The original programmer may have not had the luxury of additional time to go back and correct it. Or it just might have simply become outdated. Regardless, using software tools like Sider can support you with refactoring and creating code with confidence.  

Sider helps you to create better code, which leads to greater productivity. By analyzing your entire repository, Sider will turn your problems into measurable metrics that you can observe and fix. Not only does Sider provide an improved look at the current state of code, it also helps to improve consistency, efficiency, security, and reliability.

When refactoring with Sider, you can easily see which files need to be addressed first. Sider draws upon a combination of metrics, including lines of code and code complexity to discover which files need to be refactored. This simple visualization of your code quality can also be used as a benchmark to see the results of refactoring.

Sider also uses original linters to define custom rules and find any code that is in violation of these rules, including ensuring that naming conventions are up-to-date and fixing common spelling errors. It will also check your entire repository, giving you a bird’s eye view of any problem areas and help to ensure that your project is compliant with both standard programming rules and any custom rules unique to your project or organization. 

Once Sider has analyzed the repository, it will provide metrics on a file-by-file basis, identifying and quantifying highly complex and difficult-to-maintain code, scattered duplicate code, and much more. Sider will help you to update and refactor your legacy code with confidence. 

Creating a New Legacy

Today, when asking what is legacy code, you’re likely to receive many different modern interpretations of the term. But regardless of how your team or organization defines it, you are sure to come across it at some point in your development career. Legacy does not need to be feared, though. Instead, change the way you approach legacy code. Look beyond the obvious lines of code and find possible reasons why the code may have been written the way it was. Then, you can manage your legacy code with refactoring and testing, and by taking advantage of software solutions like Sider.  This will not only help you to greatly surpass the basic level of clean code — You’ll become a clean code connoisseur. Clean code leads to more efficient programs, happier employees, and a healthier bottom line for your business. That’s a legacy you can be proud of.

Hiroo Kato

Hiroo is responsible for marketing and messaging. He has 15 years of experience in education and tech consulting and joined Sider while pursuing technology ventures in the field of education. Hiroo holds an MA from Oxford University and is a Certified Scrum Product Owner.

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