Peter Scott-Perl Medic: Transforming Legacy Code
Addi--n-Wesley Professional | ISBN: 0201795264 | PDF | 336 pages | 6.7 MB
This book is about taking over Perl code, whether written by someone else or by yourself at an earlier time.
Developers regularly estimate that they spend 60 to 80 percent of their time working with existing code. Many problems of code inheritance are common to all languages, but the nature of the language makes Perl especially tricky. The reason why is that Perl is similar to English - bursting with irregular verbs, consistent only when it``s convenient, borrowing terms from other languages, and providing many ways to say the same thing. In fact, Perl developers have a motto with the abbreviation TMTOWTDI: There``s More Than One Way To Do It. While this flexibility is one of the language``s strengths, it also makes it extremely difficult when you are faced with an existing piece of code. There are millions of lines of Perl code being used all over the Web; much of it was built on an ad hoc basis, the creators never imagining that the code would still be in use months or years later. This book will be the resource all Perl programmers need to understand someone else``s code, even when it``s bad; repair it; convert it to a better style; upgrade it to the latest version of Perl; maintain it; and find and fix its bugs.
Perl ranks among hackers`` favorite languages-there``s always another approach to a problem, always optimization to be done, and forever new techniques to try. Perl``s a hoot. But the culture of tinkering that surrounds Perl has resulted in a large body of hard-to-understand legacy code. That legacy code has to be maintained, extended, and adapted to new conditions-often without the help of the person who originally created it. Perl Medic considers Perl from the perspective of a programmer looking at code written by someone else and trying to answer the ancient question: "What were they thinking?"
It``s a creative approach, and one that makes good reading for someone well-versed in Perl programming (author Peter Scott makes the analogy of becoming fluent in a human language, such as French, then studying its various accents and dialects). He shows, for example, a kludgy piece of code that``s meant to catch CGI form uploads, then indicates that the obvious replacement is the CGI.pm module. Elsewhere, Scott shows why symbolic references are bad, and how to avoid them by means of hashes. Some of the value in this book is in the form of documentation of the differences among Perl versions; other useful coverage deals with warnings and strictness control as debugging tools. Read this straight through to improve your own code; use the index to help decipher and improve what someone else has written. -David Wall
Topics covered: How to write good Perl code, read bad Perl code, and convert bad Perl code into good in less time that would be required to write an equivalent replacement program from scratch. Testing, debugging, documenting, replacing custom code with CPAN modules, and embracing features that became available in later versions of Perl are all covered. Overall, the author endorses and generally explains the principles of Extreme Programming (XP) for Perl work.
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