Modifying Legacy Code? How to Avoid Breaking Functionality

Modifying Legacy code

It could be possible that you might believe that completely rewriting legacy code from scratch is the only way when modifying legacy code. For example, quite a few clients we worked with for legacy code modification and optimization had similar suppositions before they got us on board.

But definitely, rewriting all the code from scratch might not be the most efficient way to go about updating legacy code. In fact, it might not be monetarily economical and would be extremely time-consuming.

Therefore, we decided to put together this article on the modification of legacy code for you if you are planning to modify legacy code in your business. Our objective is to lay down our thoughts for an optimum approach for code reusability in Object-Oriented Programming (OOP).

So what are the best tips to adhere to when modifying legacy code? Dive in to find out, but before that, let’s understand what legacy code is all about. 

What is Legacy Code?

Source code passed down from a previous developer or a previous iteration of the product is referred as legacy code. It may simply imply a codebase that supports anything that is out of date.

Dealing with legacy code entails editing or improving older code that you didn’t write but inherited. And one of the reasons why you are working on this code is to make them optimal and compatible with modern-day software compared to newer platforms.

There is no doubt that managing a codebase written by someone else can be a daunting task. And you must be careful to avoid breaking functionality. Therefore, when enhancing the codebase, take the necessary precautions.

This is not one of those problems you fix quickly, as there may be dependencies in the code you need to understand their functionality. 

Code reusability in OOP is all about using already written code to address issues. One method of code reuse is to employ OOP features like inheritance, interfaces, polymorphism, traits, etc.

So how do you go about the business of modifying legacy codes?

Modifying Legacy Code: What You Should be Doing to Avoid Breaking Functionality 

Modifying legacy code without an expert consultant could be a lot of hit and trial. However, following these points will definitely make your process much easier.

1. Make it a Habit to Review Documentation

Assessing the documentation for the initial requirements can help you discover more about the code’s beginnings.

Before making any changes to the legacy code, you should be aware of the history of any data or libraries that are a part of it. If you reread the original requirements documentation, it will be simpler for you to understand. If you can get through this procedure, you might be able to improve the code without endangering the system.

When you don’t comprehend the source and assume a piece of code is performing the task it purports to be performing, you run the risk of introducing distasteful behavior.

2. Run Test 

Testing old code enables you to learn what the code truly accomplishes. It is a faster way to detect the particular function that has to be optimized.

Legacy codebases are typically enormous and intricate. Focus on “large” tests like integration and functionality tests. You avoid the stress of having to test a particular loop, method, or class. You can learn more about legacy code by using more test alternatives like characterization tests, unit tests, end-to-end tests, and performance tests. More on this, in the ‘Refactor Legacy code’ section.

Hence, once you have a better grasp of the code, you can make changes with more confidence.

3. Don’t Rewrite the Legacy Code  

When working with legacy code, you must determine where to focus your efforts because time and energy are limited resources. It’s critical to plan and have a purpose; you need to know what can be changed and what should be ignored.

The temptation to rewrite an inherited codebase exists. But it’s frequently an error. You might occasionally believe that rewriting these programs will help you grasp what each line of code performs.

Rewriting code is time-consuming and may result in the introduction of new bugs. Or it can disable any hidden features. Refactoring the code is preferable to completely rewriting it.

4. Refactor Legacy Code 

Refactoring refers to the process of making modifications to a software system that improves its internal organization without changing the code’s external behavior. Instead of changing the functionality of the code, refactoring modifies its structure.

It is a methodical approach to code cleanup that reduces the possibility of adding errors. This endeavor simplifies the code and makes it cleaner.

It involves rewriting command methods, simplifying and combining variables, and optimizing code to make it more discernible, maintainable, and flexible.

You may need to test your code after refactoring to make sure the changes won’t disrupt the general services or have an impact on the desired behavior. We mentioned in our point 2 names “Run tests” how you can use different kinds of tests to check the functionality. These test strategies include unit tests, integration tests, and others.

For example, if you prefer to unit test a legacy code during refactoring, ensure you test code bit by bit but it does not necessarily mean testing one class only. You might want to test them together if you have a group of classes that come together to give a single functionality. This can be done with integration tests.

5. Read Code Comments and Collaborate with Other Senior Developers

Reading code comments on the legacy code you are working on is one of the best ways to get started with the legacy code. 

Almost all code bases include a README file that describes how, when, and where the project is intended to operate. By reading it, you’ll gain a place to start and a sense of what the original creator intended for the codebase.

Once more, working with other developers might put you in touch with programmers familiar with that codebase.

You might comprehend things more clearly if you have someone guide you. Who knows, you might be able to link up with developers who previously contributed to a similar codebase.

6. Try to Extract Methods

When it comes to modifying legacy code without running the risk of losing functionality, extract methods offer the best value.

When using the Extract Method, you can take a piece of code that can be grouped, transfer it into a different class, and then swap out the previous code with a call to the new method. The extract method allows you to transfer a section of code from an existing method into a new method with a name that describes what it is doing.

The extract method encourages code reuse, which significantly raises the standard of the code.

Conclusion – Modifying Legacy code

Modifying legacy codes isn’t always simple, and it takes optimism to find solutions. An inherited code result requires tremendous optimization skills from a programmer if it must adapt to new features and functionalities. Therefore, while your team and you are much more equipped to handle legacy codes now that you have read this, it is always better to bring on board legacy code optimization experts like us at Wolf-Tech.

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