What is the legacy code? Or when do we call some code or part of code is legacy?

• That code or part of code is not documented.
• Part of them used old or unsupported technology.
• You wrote that just to make it worked and not tested at all.
• You inherited that code from someone who wrote it with ignorance and in hurry.

Why is legacy code existed in the first time?

• Technical debt
• Forgotten technology
• ignorance

Fixing legacy codes

Use this loop:

• Refactor
• Unit test
• Approve

What is refactoring ?

Is a control technique for improving the design on an existin code base.

Why should we refactor?

• To understand the logic of the code base. What it did, input, output. And then you can make it readable with clean code principles.
• To change the code without break it logic. It might take long time first but then you can change it in a short of time.
• To improve the performance of the program.
• Make it more efficient. When fixing legacy code you should not focus on performance. Only focus on it when client require it.
• Refactor when you need to improve or add more functionality.
• Refactor when you need to change or improve technology.

Unit test

• Prevents regressions
• Verification
• Documentation

Approval testing

• Compare both features with legacy code and refactor code.
• Assert new test
• Lets the client approve

What are results after refactor ?

• Have cleaner structure
• Longer code or Shorter code but not change the logic of code base.
• In the future, others can easy implement new functions
• Easy documentation to understand