提升Perl编程实践：打造可维护的代码

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"Perl Best Practices" 是一本由 Damian Conway 编写的书籍，旨在帮助程序员编写更易维护、高效且风格统一的 Perl 代码。书中强调了遵循规则、约定、标准和实践的重要性，尤其是在 Perl 这种支持多种实现方式的语言中，统一的编码风格能促进团队间的沟通与协作。书中提出了256条关于代码布局、命名规范、数据和控制结构的选择、程序分解、接口设计与实现、模块化、面向对象编程、错误处理、测试和调试等方面的指导原则。这些原则的目的是使代码清晰、健壮、高效、易于维护且精炼。作者 Conway 并不声称这些是唯一正确的最佳实践，而是基于实际编程经验提出的实用建议，而非纯理论性的构想。 Conway 博士的写作风格幽默，他以丰富的实战经验和全球开发者广泛采用的实践为基础，提供了真正有效的指导。这本书不仅仅是针对 Perl 的最佳实践，还反映了如何在实际工作中有效地解决问题和表达解决方案的理念。读者可以从中学习到如何写出既能完成任务又不会造成障碍的代码，从而提升自己的编程技能和专业素养。书中的内容涵盖了多个方面，例如： 1. **代码布局**：讨论如何组织代码以提高可读性，包括缩进、空格、换行等。 2. **命名规范**：如何选择变量、函数和类名，以确保命名具有描述性和一致性。 3. **数据和控制结构**：何时使用哪种数据结构（如数组、哈希等）以及循环结构的选择。 4. **程序分解**：模块化编程的概念，将大型程序拆分为小而独立的部分。 5. **接口设计与实现**：创建简洁、明确的 API，以便其他程序员可以轻松地使用你的代码。 6. **面向对象编程**：Perl 中的 OOP 实践，包括类的设计、继承和多态性。 7. **错误处理**：如何有效地捕获和处理程序中的错误，以提高代码的健壮性。 8. **测试和调试**：自动化测试的策略和调试技巧，以确保代码的正确性。 “Perl Best Practices”是一本对于想要提升 Perl 编程水平的专业人士来说不可或缺的参考书，它不仅提供了实用的编码指导，还促进了整个编程社区的最佳实践共享。

This is the Title of the Book, eMatter Edition

Preface

This book is designed to help you write better Perl code: in fact, the best Perl code

you possibly can. It’s a collection of 256 guidelines covering various aspects of the art

of coding, including layout, name selection, choice of data and control structures,

program decomposition, interface design and implementation, modularity, object

orientation, error handling, testing, and debugging. These guidelines have been

developed and refined over a programming career spanning 22 years. They’re

designed to work well together, and to produce code that is clear, robust, efficient,

maintainable, and concise.

Mind you, that’s not easy to achieve. Conciseness can be the natural enemy of clar-

ity; efficiency the nemesis of maintainability. And armouring code to make it suffi-

ciently robust can undermine clarity, efficiency, conciseness, and maintainability.

Sometimes it’s a case of: “Choose any one.”

This book doesn’t try to offer the one true universal and unequivocal set of best prac-

tices. There are as many ways of measuring code quality, and as many dimensions in

which code can be judged, as there are programmers to make those assessments.

Each programmer and each programming team will have their own opinions about

the most important and desirable attributes of code.

What this book offers instead is a set of best practices: a set that is coherent, widely

applicable, balanced in its aims, and that is based on real-world experience of how

code is actually written, rather than on someone’s ivory-tower theories on how code

ought to be created. Most of all, it’s a set of practices that actually work, and that

many developers around the world are already using. Much like Perl itself, these

guidelines are about helping you to get your job done, without getting in the way.

If you’re an experienced developer, it’s almost certain that you won’t like all of the

suggestions that follow. You will find some of them unnatural or counterintuitive;

others may feel excessively rigid and un-Perlish. Maybe they’ll just seem unnecessar-

ily different from the ways you’re used to writing software, and from the long-

ingrained coding habits you find so comfortable.

This is the Title of the Book, eMatter Edition

xvi

Preface

Try to put those feelings aside as you read through the advice in this book. Review it

as you would any other proposed code enhancement: analyze the arguments that are

made for these new practices; ask yourself whether you’ve ever fallen into the traps

they seek to avoid; consider whether the coding techniques suggested here might be

worth trying.

Just thinking about these issues—becoming conscious of the way you currently write

code—can be of enormous benefit, even if you don’t adopt a single one of the recom-

mendations that follow.

Contents of This Book

Chapter 1, Best Practices, explains why it might be worth reassessing your current

coding practices. It discusses how coding styles are evolved, and sets out three broad

criteria against which any existing or proposed coding practice can be assessed. The

chapter also explains why good coding habits matter and suggests how they can be

developed.

Chapter 2, Code Layout, tackles the many contentious issues of code layout. It sug-

gests how to set out block delimiters; how to visually distinguish built-ins and key-

words from subroutines and variables; where to place operators, terminators,

delimiters, and other punctuation; how to improve readability by the consistent use

of whitespace; the optimal width for code lines and block indents; how to set out

lists of values; and where to break long expressions. It concludes by recommending a

convenient tool that automates most of these layout tasks.

Chapter 3, Naming Conventions, presents a series of guidelines that can help you

choose more descriptive names for variables, subroutines, and namespaces. It also

demonstrates how the various components of a consistent naming scheme can work

together to improve the overall maintainability of code, both by making it more read-

able and by reducing the need for deobfuscatory comments.

Chapter 4, Values and Expressions, provides a simple set of rules that can help you

avoid common pitfalls when creating character strings, numbers, and lists. Topics

include how to avoid unintended variable interpolation (and non-interpolation), reli-

able and readable approaches to nonprintable characters, defining constants, avoid-

ing barewords, and taming heredocs, commas, long numbers, and lists.

Chapter 5, Variables, explores a robust approach to using variables. It explains the

inherent drawbacks of package or punctuation variables, suggesting safer alterna-

tives where possible, and safer practices where there are no alternatives. The second

half of the chapter presents several efficient and maintainable techniques of handling

data in arrays and hashes using the “container slicing” mechanism.

Chapter 6, Control Structures, examines Perl’s rich variety of control structures,

encouraging the use of those that are easier to maintain, less error-prone, or more

This is the Title of the Book, eMatter Edition

Preface

xvii

efficient. The chapter provides a set of simple guidelines for deciding which of for,

while,ormap is most appropriate for a given task. The effective use of iterator vari-

ables is also discussed, including the common case of needing to iterate hash entries

by key and value simultaneously.

Chapter 7, Documentation, suggests a series of techniques that can make document-

ing your code less tedious, and therefore more likely. It advocates a template-based

approach to both user and technical documentation, and discusses when, where, and

how to write useful and accurate comments.

Chapter 8, Built-in Functions, discusses better ways of using some of Perl’s most pop-

ular built-in functions, including

sort, reverse, scalar, eval, unpack, split, substr,

values, select, sleep, map, and grep. It also summarizes the many other useful “non-

built-in” builtins provided by two modules from the standard Perl distribution and

one from CPAN.

Chapter 9, Subroutines, describes efficient and maintainable ways to write subrou-

tines in Perl, including the use of positional, named, and optional arguments, argu-

ment validation and defaults, safe calling and return conventions, predictable return

values in various contexts, and why subroutine prototypes and implicit returns

should be avoided.

Chapter 10, I/O, explains how to open and close files reliably, when to use line-based

input, how to correctly detect interactive applications, the importance of prompting,

and how best to provide feedback to users during long non-interactive tasks.

Chapter 11, References, offers advice on demystifying Perl’s many dereferencing syn-

taxes, discusses why symbolic references create more problems than they solve, and

recommends ways to prevent cyclic reference chains from causing memory leaks.

Chapter 12, Regular Expressions, presents guidelines for using regular expressions. It

recommends the use of extended formatting, suggests a simple but unusual fix for

Perl’s confusing “single-line” and “multiline” matching modes, warns of the perils of

matching whitespace too precisely, shows how to avoid using the error-prone

numeric variables, presents a robust approach to building complex regexes that are

still maintainable, gives several hints on optimizing slow matches, and concludes by

explaining when not to use regular expressions.

Chapter 13, Error Handling, advocates a coherent exception-based approach to error

handling, and explains why exceptions are preferable to special return values or

flags. It also recommends the use of exception objects, and explores in detail how

they can be declared, created, thrown, caught, and handled.

Chapter 14, Command-Line Processing, addresses the design and implementation of

command-line interfaces, both for individual programs and for application suites. It

recommends several modules that can make your command-line interfaces more

consistent and predictable, and at the same time can considerably reduce the effort

required to implement those interfaces.

This is the Title of the Book, eMatter Edition

xviii

Preface

Chapter 15, Objects, and Chapter 16, Class Hierarchies, offer a robust and efficient

approach to creating objects and class hierarchies in Perl. This approach provides fully

encapsulated objects with no performance penalty, and supports single and multiple

inheritance without the usual problems of attribute collision, incomplete initialization,

partial destruction, or incorrect method autoloading. Chapter 16 also introduces a new

module that allows these robust and efficient classes to be built semi-automatically.

Chapter 17, Modules, looks at non-object-oriented modules, exploring the best ways

to create them, design their interfaces, declare and check their version numbers, and

refactor existing code into them. This chapter also discusses the many existing mod-

ules that are freely available as part of the Perl standard library and on CPAN.

Chapter 18, Testing and Debugging, encourages the use of testing, advocating test-

driven design and development using the core

Test:: modules. It also offers tips on

effective debugging techniques, including a description of various modules and other

free tools that can make debugging easier.

Chapter 19, Miscellanea, offers several additional guidelines on miscellaneous topics

such as revision control, interfacing to code written in other languages, processing

configuration files, text formatting, tied variables, benchmarking and profiling your

code, caching techniques, and some general advice on refactoring.

Appendix A, Essential Perl Best Practices, summarizes the 30 most important guide-

lines in the book in three one-page lists. Appendix B, Perl Best Practices, lists all 256

guidelines, with cross-references to their chapters and locations. Appendix C, Editor

Configurations, provides some useful configuration options for the Vim, Vile, Emacs,

TextWrangler, and BBEdit text editors. Appendix D, Recommended Modules and

Utilities, lists and cross-references the various modules recommended throughout the

book, and provides a brief summary of their most useful subroutines. Appendix E

offers a short bibliography.

Conventions Used in This Book

The following typographical conventions are used in the text of this book:

Italic

Indicates emphasis, new terms, URLs, email addresses, filenames, paths, and

Unix utilities.

Constant-width regular

Indicates commands, variables, attributes, functions, classes, namespaces, meth-

ods, modules, values, the contents of files, the output from commands, and code

examples that break recommended practices.

Constant-width bold

Indicates commands and other text that should be typed literally by the user,

and code examples that demonstrate recommended practices.

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