How to refactor a Delphi unit with 10000 lines with no documentation?

Question

I have been assigned the task to refactor a Delphi unit. Wow. 10000 lines of code, no documentation, tons of copy and paste code.

THere are many methods made with copy a

Answer 1

I've faced similar situations. My condolences to you!

In my opinion, the most important thing is that you actually understand all the code as it is today. Minds better than mine may be able to simply read the code and understand it. However, I can't.

After reading the code for a general overview, I usually repeatedly single step through it in the debugger until I begin to see some patterns of operation and recognize code that I've read before. Maybe this is obvious, but thought I'd mention it.

You might also think about creating a good test suite that runs on the current code.

Answer 2

Does the interface section contain a bunch of class definitions? If so, create a new unit for every class and move each class to it's own unit.
If you use Delphi 2007 or better, you can use the "refactor/Move" option to move those classes to the new (namespace) units.
The next step is splitting the large classes into smaller classes. That's just a lot of manual work.
Once your code is divided over multiple units, you can examine each unit, detect identical code and generate base classes that would be used as parent for the two classes that share similar functionality.

Answer 3

I would use some sort of UML tool to generate som class diagrams and other diagrams to get an overview of the system, and start splitting up and commenting like @Workshop Alex said.

Answer 4

In addition of understanding the code etc, these tools may help refactoring and reorganizing the project:

Model Maker is powerful design, reverse-engineer and refactoring tool: http://www.modelmakertools.com/modelmaker/index.html

Model Maker Code Explorer is powerful plugin for Delphi IDE to help with refactoring, code navigation etc: http://www.modelmakertools.com/code-explorer/index.html

Answer 5

Use a tool like Doxygen to help you map the code.

Help on that is here

Answer 6

1. Get yourself a copy of Working Effectively with Legacy Code by Micheal Feathers. It has all kinds of techniques for safely refactoring code to get it running under a test framework. Examples are mostly in Java and C++ but should be easy enough to figure out.
2. Install a third-party refactoring tool (or multiple) such as CodeRush for Delphi(sadly no longer developed), Castalia or ModelMaker Code Explorer. Delphi has some refactoring support built in but in my experience it is too limited and tends to choke on very large code bases.
3. Buy a copy of Simian. It doesn't have direct support for Object Pascal but its plain text parser works well enough. If enough people request support for Object Pascal I'm sure they'd add it. I haven't found any other code duplication detection tool as capable as Simian.

I would also recommend bookmarking http://www.refactoring.com/catalog/ and http://www.industriallogic.com/xp/refactoring/catalog.html.

It also wouldn't hurt to get a copy of Clean Code: A Handbook of Agile Software Craftsmanship by Robert "Uncle Bob" Martin et al. It's easy to recognize bad code. It's much harder know when you're writing good code.

A word of caution: Focus on refactoring the code you need to work on. Its easy to start down the rabbit hole and wind up spending months refactoring code that wasn't immediately relevant to the task at hand.

And save your self some trouble. Don't try to "fix" code and refactor it at the same time. Refactor first, then fix bugs or add that new feature. Remember, refactoring is modifying without changing external behavior.

Resist the urge to attempt a complete rewrite. I learned the hard way that crappy code that meets the user's requirements is preferable to clean code that doesn't. Crappy code can always be incrementally improved until its something to be proud of.