. 16. Power Editing
17. Source Code Control
18. Debugging
19. Text Manipulation
20. Code Generators
4 PRAGMATIC PARANOIA
21. Design by Contract
22. Dead Programs Tell No Lies
23. Assertive Programming
24. When to Use Exceptions
25. How to Balance Resources
5 BEND, OR BREAK
26. Decoupling and the Law of Demeter
27. Metaprogramming
28. Temporal Coupling
29. It's Just a View
30. Blackboards
6 WHILE You ARE CODING
31. Programming by Coincidence
32. Algorithm Speed
33. Refactoring
34. Code That's Easy to Test
35. Evil Wizards
7 BEFORE THE PROJECT
36. The Requirements Pit
37. Solving Impossible Puzzles
38. Not Until You're Ready
39. The Specification Trap
40. Circles and Arrows
8 PRAGMATIC PROJECTS
41. Pragmatic Teams
42. Ubiquitous Automation
43. Ruthless Testing
44. It's All Writing
45. Great Expectations
46. Pride and Prejudice
Appendices
A RESOURCES
Professional Societies
Bufiding a Library
Internet Resources
Bibliography
B ANSWERS TO EXERCISES
INDEX

. Jack of all trades. You try hard to be familiar with a broad range of technologies and environments, and you work to keep abreast of new developments. Although your current job may require you to be a specialist, you will always be able to move on to new areas and new challenges.
We've left the most basic characteristics until last. All Pragmatic Programmers share them. They're basic enough to state as tips: We feel that there is no point in developing software unless you care about doing it well.
In order to be a Pragmatic Programmer, we're challenging you to think about what you're doing while you're doing it. This isn't a one-time audit of current practices---it's an ongoing critical appraisal of every decision you make, every day, and on every development. Never run on
auto-pilot. Constantly be thinking, critiquing your work in real time. The old IBM corporate motto, THINK!, is the Pragmatic Programmer's mantra.
If this sounds like hard work to you, then you're exhibiting the rea//st/c characteristic. This is going to take up some of your valuable time--time that is probably already under tremendous pressure. The reward is a more active involvement with a job you love, a feeling of mastery over
an increasing range of subjects, and pleasure in a feeling of continuous improvement. Over the long term, your time investment will be repaid as you and your team become more efficient, write code that's easier to maintain, and spend less time in meetings.
Individual Pragmatists, Large Teams
Some people feel that there is no room for individuality on large teams or complex projects. "Software construction is an engineering discipline," they say, "that breaks down ff individual team members make decisions for themselves."
We disagree.
The construction of software should be an engineering discipline. However, this doesn't preclude individual craftsmanship. Think about the large cathedrals built in Europe during the Middle Ages. Each took thousands of person-years of effort, spread over many decades. Lessons learned were passed down to the next set of builders, who advanced the state of structural engineering with their accomplishments. But the carpenters, stonecutters, carvers, and glass workers were all craftspeople, interpreting the engineering requirements to produce a whole that transcended the purely mechanical side of the construction. It was their belief in their individual contributions that sustained the projects:
We who cut mere stones must always be envisioning cathedrals. Quarry worker's creed
Within the overall structure of a project there is always room for individuality and craftsmanship. This is particularly true given the current state of software engineering. One hundred years from now, our engineering may seem as archaic as the techniques used by medieval
cathedral builders seem to today's civil engineers, while our craftsman-ship will still be honored.
It's a Continuous Process
A tourist visiting England's Eton College asked the gardener how he got the lawns so perfect. "That's easy," he replied, "You just brush off the dew every morning, mow them every other day, and roll them once a week. "
"Is that all?" asked the tourist.
"Absolutely," replied the gardener. "Do that for 500 years and you'll have a nice lawn, too." Great lawns need small amounts of daily care, and so do great programmers. Management consultants like to drop the word kaizen in conversations. "Kaizen" is a Japanese term that captures the concept of continuously making many small improvements. It was considered to be one of the main reasons for the dramatic gains in productivity and quality in Japanese manufacturing and was widely copied throughout the world. Kaizen applies to individuals, too. Every day, work to refine
the skills you have and to add new tools to your repertoire. Unlike the Eton lawns, you'll start seeing results in a matter of days. Over the years, you'll be amazed at how your experience has blossomed and your skills have grown.
How the Book Is Organized
This book is written as a collection of short sections. Each section is self-contained, and addresses a particular topic. You'll find numerous cross references, which help put each topic in context. Feel free to read the sections in any order--this isn't a book you need to read front-to-back.
Occasionally you'll come across a box labeled Tip nn (such as Tip 1,"Care About Your Craft" on page xix). As well as emphasizing points in the text, we feel the tips have a life of their own--we live by them daffy. You'll find a summary of all the tips on a pull-out card inside the back cover.
Appendix A contains a set of resources: the book's bibliography, a list of URLs to Web resources, and a list of recommended periodicals, books, and professional organizations. Throughout the book you'll find references to the bibliography and to the list of URLs---such as [KP99] and
[URL 18], respectively. We've included exercises and challenges where appropriate. Exercises
normally have relatively straightforward answers, while the challenges are more open-ended. To give you an idea of our thinking, we've included our answers to the exercises in Appendix B, but very few have a single correct solution. The challenges might form the basis of group discussions or essay work in advanced programming courses.
What's in a Name?
"When I use a word," Humpty Dumpty said, in rather a scornful tone, "it means just what I choose it to mean--neither more nor less."
Carroll, Through the Looking-Glass
Scattered throughout the book you'll find various bits of jargon--either perfectly good English words that have been corrupted to mean something technical, or horrendous made-up words that have been assigned meanings by computer scientists with a grudge against the language. The first time we use each of these jargon words, we try to define it, or at least give a hint to its meaning. However, we're sure that some have fallen through the cracks, and others, such as object and relational database, are in common enough usage that adding a definition would be boring. If you do come across a term you haven't seen before, please don't just skip over it. Take time to look it up, perhaps on the Web, or maybe in a computer science textbook. And, if you get a chance, drop us an e-mail and complain, so we can add a definition to the next edition.
Having said all this, we decided to get revenge against the computer scientists. Sometimes, there are perfectly good jargon words for concepts, words that we've decided to ignore. Why? Because the existing jargon is normally restricted to a particular problem domain, or to a particular phase of development. However, one of the basic philosophies of this book is that most of the techniques we're recommending are universal: modularity applies to code, designs, documentation, and team organization, for instance. When we wanted to use the conventional
Jargon word in a broader context, it got confusing-we couldn't seem to overcome the baggage the original term brought with it. When this happened, we contributed to the decline of the language by inventing our own terms.
Source Code and Other Resources
Most of the code shown in this book is extracted from compfiable source files, available for download from our Web site:
www.pragmat icprogr ammer.c om
There you'll also find links to -resources we find useful, along with updates to the book and news of other Pragmatic Programmer developments.
Send Us Feedback
We'd appreciate hearing from you. Comments, suggestions, errors in the text, and problems in the examples are all welcome. E-mail us at
ppbook@pragmaticprogrammer, com
Acknowledgments
When we started wriUng this book, we had no idea how much of a team effort it would end up being.
Addison-Wesley has been brilliant, taking a couple of wet-behind-the-ears hackers and walking us through the whole book-production process, from idea to camera-ready copy. Many thanks to John Wait and Meera Ravindiran for their initial support, Mike Hendrickson, our enthusiastic editor (and a mean cover designer!), Lorraine Ferrier and John Fuller for their help with production, and the indefatigable Julie DeBaggis for keeping us all together.
Then there were the reviewers: Greg Andress, Mark Cheers, Chris Clee land, Alistair Cockburn, Ward Cunningham, Martin Fowler, Thanh T. Glang, Robert L. Glass, Scott Henninger, Michael Hunter, Brian Kirby, John Lakos, Pete McBreen, Carey P. Morris, Jared Richardson, Kevin Ruland, Eric Starr, Eric Vought, Chris Van Wyk, and Deborra Zukowski. Without their careful comments and valuable insights, this book would be less readable, less accurate, and twice as long. Thank
you all for your time and wisdom.
The second printing of this book benefited greatly from the eagle eyes of our readers. Many thanks to Brian Blank, Paul Boal, Tom Ekberg, Brent Fulgham, Louis Paul Hebert, Henk-Jan Olde Loohuis, Alan Lund, Gareth McCaughan, Yoshiki Shibata, and Volker Wurst, both for find-
ing the mistakes and for having the grace to point them out gently. Over the years, we have worked with a large number of progressive clients, where we gained and refined the experience we write about here. Recently, we've been fortunate to work with Peter Gehrke on sev-
eral large projects. His support and enthusiasm for our techniques are much appreciated.
This book was produced using LATEX, pic, Perl, dvips, ghostview, ispell, GNU make, CVS, Emacs, XEmacs, EGCS, GCC, Java, iContract, and SmaUEiffel, using the Bash and zsh shells under Linux. The staggering thing is that all of this tremendous software is freely available. We
owe a huge "thank you" to the thousands of Pragmatic Programmers worldwide who have contributed these and other works to us all. We'd particularly like to thank Reto Kramer for his help with iContract. Last, but in no way least, we owe a huge debt to our famfiies. Not only have they put up with late night typing, huge telephone bills, and our permanent air of distraction, but they've had the grace to read what we've written, time after time. Thank you for letting us dream.
Andy Hunt
Dave Thomas