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Working Effectively with Legacy Code
Merlin42 writes "I recently took a Test-Driven-Development (TDD) training course and the teacher recommended that I read "Working Effectively with Legacy Code" by Michael Feathers. First things first, a note about the title. Feathers defines "Legacy Code" a bit different than you may expect, especially if you are not into the XP/Agile/TDD world. I have heard (and used) a number of definitions for "legacy code" over the years. Most of these definitions have to do with code that is old, inherited, difficult to maintain, or interfaces with other 'legacy' hardware/software. Feathers' definition is 'code without tests.' For those not into TDD this may seem odd, but in the TDD world, tests are what make code easy to maintain. When good unit tests are in place, then code can be changed at will and the tests will tell automatically you if you broke anything." Read on for the rest of Kevin's review.
Working Effectively with Legacy Code
author
Michael Feathers
pages
456
publisher
Prentice Hall
rating
9/10
reviewer
Kevin Fitch
ISBN
978-0-13-117705-5
summary
Excelent overview of how to apply TDD to an existing project
Overall this is definitely an interesting read, and useful to anyone who has ever yelled "FSCKing LEGACY code!" It will be most useful to someone who already has some appreciation for TDD and wants to use it to 'pay down the technical debt' in a legacy code project. In my opinion adding unit tests (a sort of retroactive TDD) is the best ... err ... most effective approach for getting a legacy code project into a more malleable state.
One caveat is that most of the book is focused on working with object oriented programming languages. There is some coverage of techniques for procedural languages (mainly C), but this is not the main focus of the book. In a way this is unfortunate, since there is a lot of really useful C code out there gathering dust. But in the book he states that "the number of things you can do to introduce unit tests in procedural languages is pretty small." Unfortunately I would have to agree with him on this point.
One of the greatest things about this book is that it is written by someone who has worked with a lot of legacy code, and there are numerous real world anecdotes sprinkled throughout the text that really serve to help drive the points home. The code examples are plentiful, but not verbose. They all look like real code you might find lurking in a dark corner at work, not some fanciful made up snippet.
The high level goal of the book is show you how to write good unit tests for code that wasn't designed with unit tests in mind. The first step for writing unit tests is getting individual classes or functions into a test harness where you can apply known inputs, and check the outputs or behavior. To do this you need to break dependencies in the original code. The bulk of the book is dedicated to looking at different approaches to breaking dependencies.
Much of the book is organized like a FAQ. There are chapter titles like: "I Need to Make a Change. What Methods Should I Test?" and "My Project Is Not Object Oriented. How Do I Make Safe Changes?". This organization makes the book work a bit better as reference than as learning material. After the first few chapters there is very little flow to the book. Each chapter tends to stand as an independent look into a particular problem common in legacy code. As a result, you can read the table of contents and usually skip to a self-contained chapter that will help with the problem at hand.
The final chapter of the book is a listing of all the refactoring techniques used throughout the rest of book. So if you have a particular dependency-breaking technique in mind, you can skip straight to the description of the technique you want to use. This can be quite helpful when you need to perform a refactoring before you can get your code into a test harness. The descriptions are straightforward and provide a little checklist at the end that will help you make sure you didn't miss anything.
In conclusion I would definitely recommend this book to a colleague who is trying to introduce unit tests into code that was not designed with testing in mind. In fact I have already lent the book to several people at work, most of whom have bought their own copy.
You can purchase Working Effectively with Legacy Code from amazon.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
One caveat is that most of the book is focused on working with object oriented programming languages. There is some coverage of techniques for procedural languages (mainly C), but this is not the main focus of the book. In a way this is unfortunate, since there is a lot of really useful C code out there gathering dust. But in the book he states that "the number of things you can do to introduce unit tests in procedural languages is pretty small." Unfortunately I would have to agree with him on this point.
One of the greatest things about this book is that it is written by someone who has worked with a lot of legacy code, and there are numerous real world anecdotes sprinkled throughout the text that really serve to help drive the points home. The code examples are plentiful, but not verbose. They all look like real code you might find lurking in a dark corner at work, not some fanciful made up snippet.
The high level goal of the book is show you how to write good unit tests for code that wasn't designed with unit tests in mind. The first step for writing unit tests is getting individual classes or functions into a test harness where you can apply known inputs, and check the outputs or behavior. To do this you need to break dependencies in the original code. The bulk of the book is dedicated to looking at different approaches to breaking dependencies.
Much of the book is organized like a FAQ. There are chapter titles like: "I Need to Make a Change. What Methods Should I Test?" and "My Project Is Not Object Oriented. How Do I Make Safe Changes?". This organization makes the book work a bit better as reference than as learning material. After the first few chapters there is very little flow to the book. Each chapter tends to stand as an independent look into a particular problem common in legacy code. As a result, you can read the table of contents and usually skip to a self-contained chapter that will help with the problem at hand.
The final chapter of the book is a listing of all the refactoring techniques used throughout the rest of book. So if you have a particular dependency-breaking technique in mind, you can skip straight to the description of the technique you want to use. This can be quite helpful when you need to perform a refactoring before you can get your code into a test harness. The descriptions are straightforward and provide a little checklist at the end that will help you make sure you didn't miss anything.
In conclusion I would definitely recommend this book to a colleague who is trying to introduce unit tests into code that was not designed with testing in mind. In fact I have already lent the book to several people at work, most of whom have bought their own copy.
You can purchase Working Effectively with Legacy Code from amazon.com. Slashdot welcomes readers' book reviews -- to see your own review here, read the book review guidelines, then visit the submission page.
Buy Martin Fowler's Refactoring instead.
The most successful strategy I have had for legacy code that I have inherited is encapsulation of the old code into a new framework. I first attempt to build a black box wrapper with an API for what ever the legacy code did (wrap 5000 line loops, etc). Then as I can or need to change it, I take the black box and break it into proper libraries or readable functions (or start over). Have been able to do this for some really large bases of code and have a working system while I re-factored the mess a little at a time.
I have had good luck with legacy code, here is what I do:
#1 Figure out what the code does and document it with comments and write a document on it.
#2 Identify variables and objects and what they are used for and any naming convention the code may use.
#3 You need to stick to the original style of writing or rewrite parts of it into your style if it can give a performance boost or make it more stable.
#4 Try to find programming errors and things that do not make sense and rewrite them so that they make sense. Do error trapping and check for nulls and letters entered into number variables and all other sorts of things most legacy programmers overlook.
#5 Work to make the code stable and not crash and run faster before you start adding new features to it. Users don't want to wait 15 minutes to do a report and then have the program crash after their wait.
#6 Work with the help desk to identify the most serious problems that users complain about the legacy code. Make it a "wish list" and then fix each complaint as you have time to do.
#7 Get direction from your managers, tell them what you are trying to do and any problems you have. You need to work as a team with other developers, the help desk, managers, and users to work out the issues with legacy code. Explain to them when you need more time and cannot make the schedule they gave. Make a deal with them to release a stable version but lacking features that might take more time than they thought to do. Tell the users you had to no add in those features to meet a deadline or ask them if they want to wait until you figure out how to add in those features.
#8 Play Sherlock Holmes and read books or Internet web sites on the language and technology used with the legacy code. Search knowledge bases and blogs and forums for answers to solutions, sometimes someone else figured out what you are trying to solve. If not ask on a forum or blog or web site and see who answers. Many of my answers got that way from the Internet on legacy code, but management didn't understand why I spent so much time on the Internet. It was because they wouldn't buy me the books I needed and I had no documentation or anything to work with except for pure code with no comments and all with serious problems. Sometimes I had to spend 5 hours a day researching on the Internet and 3 or 4 hours coding, but in doing so I saved months of work, but management didn't understand that each web site I went to was work related and I looked at the design of sample code even HTML code to get ideas on how to solve the legacy code problems. Sometimes you have to call up a help desk of a vendor to get answers as well, but they docked me for long distance calls to Canada where Crystal Reports and Segate/Business Objects had their headquarters. Fixing Crystal Report errors would make me spend 5 hours a day on the Internet just to figure out what caused double lines in a report and why only certain users got it and not others.
#9 When in doubt ask for help. Sometimes another pair of eyes can spot errors and mistakes that you cannot see. Diversity is a good thing with team members. Form a dream team of programmers of different backgrounds for best results.
#10 When in danger, when in doubt, don't run in circles and scream and shout. Take a walk, get something to drink and relax. Take a mental health break instead of getting angry at other people for not helping you or not doing their jobs properly, they might be suffering from stress like you are and you don't know it. Be positive, not negative.
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Either you misunderstood my post, or you have a fundamental misunderstanding of the halting problem.
It says that no algorithm can decide in general whether or not a given program / input pair will halt or not. The emphasis on the in general is the key.
It is actually trivial to do in many, many specific cases.
http://en.wikipedia.org/wiki/Halting_problem
In particular, take note of the second sentence:
Alan Turing proved in 1936 that a general algorithm to solve the halting problem for all possible program-input pairs cannot exist.
(emphasis mine)
"Who is the Journal of Quantum Physics going to believe?" --Stephen Hawking