Book Description
"C++ Template Metaprogramming" sheds light on the most powerful idioms of today's C++, at long last delivering practical metaprogramming tools and techniques into the hands of the everyday programmer. Since the introduction of templates, C++ programmers have discovered surprising and powerful ways to perform computation at compile-time. While the excitement generated by these capabilities among C++ experts has reached the community at large, their practical application remains out-of-reach for many programmers. Literature on C++ template metaprogramming has focused primarily on details of low-level "tricks" at the expense of strong idioms and abstractions, and without illuminating the path from metaprogramming to expressive interfaces and efficient, maintainable software. This book delivers both "big picture" ideas and practical tools. It explains what metaprogramming is, why it matters, and how the unique combination of features in C++ make it an especially powerful language for metaprogramming. It also presents the Boost Metaprogramming Library, a powerful open source framework of high-level compile-time components based on familiar STL idioms, which makes C++ metaprogramming easy, expressive, and fun.

From the Back Cover

Practical Metaprogramming for Working C++ Developers

Using metaprogramming techniques, you can engineer software with greater quality, portability, and reusability. You can write more expressive and elegant code, and waste less time on "boilerplate." In short, you won't just be more productive: you'll have more fun, too. If you code with C++, the Boost MPL offers high-level facilities that make metaprogramming even more useful and accessible. Now, for the first time, there's a book that demystifies both metaprogramming and the Boost MPL.

Selected to write this book by C++ creator Bjarne Stroustrup, Boost MPL community leaders David Abrahams and Aleksey Gurtovoy are uniquely qualified to explain metaprogramming to experienced C++ developers. In this book, they systematically illuminate the "how," "why," and "when" of metaprogramming, thoroughly explain its advantages, and show exactly how to apply it in real-world development projects.

Coverage includes: Fundamental metaprogramming concepts: traits, type manipulation, type wrappers, and more An in-depth look at metafunctions and metafunction classes Sequences, algorithms, iterators, diagnostics, views, iterator adaptors, and more Boost MPL: motivation, usage, design, implementation, and practical examples Lessons and best practices for C++ template metaprogramming Crossing the compile-time/runtime boundary Domain-Specific Embedded Languages, including a complete DSEL design walkthrough Improving compile-time performance A Boost MPL case study in event handling

The CD-ROM contains all Boost C++ libraries, including the Boost Metaprogramming Library and reference documentation, along with all of the book's sample code and extensive supplementary material.

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About the Author

Dave Abrahams, a founding member and moderator of the Boost C++ library development group, heads Boost Consulting, a Somerville, Massachusetts company providing support and development services for the Boost C++ libraries. He has written six Boost libraries and contributed to several others. Abrahams has been an ANSI/ISO C++ committee member since 1996, when he contributed a theory, specification, and implementation of exception handling for the C++ standard library.

Aleksey Gurtovoy is a C++ developer and manager for MetaCommunications in Minnesota. He has more than a decade of experience working with C++, and often contributes articles to leading C++ newsgroups.

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Excerpt. © Reprinted by permission. All rights reserved.

In 1998 Dave had the privilege of attending a workshop in Generic Programming at Dagstuhl Castle in Germany. Near the end of theworkshop, a very enthusiastic Kristof Czarnecki and Ullrich Eisenecker (of Generative Programming fame) passed out a few pages of C++ source code that they billed as a complete Lisp implementation built out of C++ templates. At the time it appeared to Dave to be nothing more than a curiosity, a charming but impractical hijacking of the template system to prove that you can write programs that execute at compile time. He never suspected that one day he would see a role for metaprogramming in most of his day-to-day programming jobs. In many ways, that collection of templates was the precursor to the Boost Metaprogramming Library (MPL): It may have been the first library designed to turn compile-time C++ from an ad hoc collection of "template tricks" into an example of disciplined and readable software engineering. With the availability of tools to write and understand metaprograms at a high level, we've since found that using these techniques is not only practical, but easy, fun, and often astoundingly powerful.

Despite the existence of numerous real systems built with template metaprogramming and the MPL, many people still consider metaprogramming to be other-worldly magic, and often as something to be avoided in day-to-day production code. If you've never done any metaprogramming, it may not even have an obvious relationship to the work you do. With this book, we hope to lift the veil of mystery, so that you get an understanding not only of how metaprogramming is done, but also why and when. The best part is that while much of the mystery will have dissolved, we think you'll still find enough magic left in the subject to stay as inspired about it as we are.Making the Most of This Book

The first few chapters of this book lay the conceptual foundation you'll need for most everything else we cover, and chapters generally build on material that has come before. That said, feel free to skip ahead for any reason—we've tried to make that possible by providing cross-references when we use terms introduced earlier on.

Chapter 10, Domain-Specific Embedded Languages, is an exception to the rule that later chapters depend on earlier ones. It focuses mostly on concepts, and only appears late in the book because at that point you'll have learned the tools and techniques to put Domain-Specific Embedded Languages into play in real code. If you only remember one chapter by the time you're done, make it that one.

Near the end of many chapters, you'll find a Details section that summarizes key ideas. These sections usually add new material that deepens the earlier discussion,* so even if you are inclined to skim them the first time through, we suggest you refer back to them later.

We conclude most chapters with exercises designed to help you develop both your programming and conceptual muscles. Those marked with asterisks are expected to be more of a workout than the others. Not all exercises involve writing code—some could be considered "essay questions"—and you don't have to complete them in order to move on to later chapters. We do suggest you look through them, give a little thought to how you'd answer each one, and try your hand at one or two; it's a great way to gain confidence with what you've just read.Supplementary Material

This book comes with a companion CD that supplies the following items in electronic form Sample code from the book. A release of the Boost C++ libraries. Boost has become known for high-quality, peer-reviewed, portable, generic, and freely reusable C++ libraries. We make extensive use of one Boost library throughout the book—the Boost Metaprogramming Library (MPL)—and we discuss several others. A complete MPL reference manual, in HTML and PDF form. Boost libraries discussed in this book that are not yet part of an official release.

The index.html file at the top level of the CD will provide you with a convenient guide to all of its contents. Additional and updated material, including the inevitable errata, will appear on the book's Web site: http://www.boost-consulting.com/mplbook. You'll also find a place there to report any mistakes you might find.Trying It Out

To compile any of the examples, just put the CD's boost 1 32 0/ directory into your compiler's #include path.

The libraries we present in this book go to great lengths to hide the problems of less-than-perfect compilers, so it's unlikely that you'll have trouble with the examples we present here. That said, we divide C++ compilers roughly into three categories.

      A. Those with mostly conforming template implementations. On these compilers, the examples and libraries "just work." Almost anything released since 2001, and a few compilers released before then, fall into this category.
      B. Those that can be made to work, but require some workarounds in user code.
      C. Those that are too broken to use effectively for template metaprogramming.

Appendix D lists the compilers that are known to fall into each of these categories. For those in category B, Appendix D refers to a list of portability idioms. These idioms have been applied to the copies of the book's examples that appear on the accompanying CD, but to avoid distracting the majority of readers they don't appear in the main text.

The CD also contains a portability table with a detailed report of how various compilers are doing with our examples. GCC is available free for most platforms, and recent versions have no problems handling the code we present here.

Even if you have a relatively modern compiler from category A, it might be a good idea to grab a copy of GCC with which to cross-check your code. Often the easiest way to decipher an inscrutable error message is to see what some other compiler has to say about your program. If you find yourself struggling with error messages as you try to do the exercises, you might want to skip ahead and read the first two sections of Chapter 8, which discusses how to read and manage diagnostics.

And now, on to C++ Template Metaprogramming!

— Dave and Aleksey

* We borrowed this idea from Andrew Koenig and Barbara Moo's Accelerated C++: Practical Programming By Example.

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FROM THE PUBLISHER

Practical Metaprogramming for Working C++ Developers

Using metaprogramming techniques, you can engineer software with greater quality, portability, and reusability. You can write more expressive and elegant code, and waste less time on "boilerplate." In short, you won't just be more productive: you'll have more fun, too. If you code with C++, the Boost MPL offers high-level facilities that make metaprogramming even more useful and accessible. Now, for the first time, there's a book that demystifies both metaprogramming and the Boost MPL.

Selected to write this book by C++ creator Bjarne Stroustrup, Boost MPL community leaders David Abrahams and Aleksey Gurtovoy are uniquely qualified to explain metaprogramming to experienced C++ developers. In this book, they systematically illuminate the "how," "why," and "when" of metaprogramming, thoroughly explain its advantages, and show exactly how to apply it in real-world development projects.

Coverage includes: Fundamental metaprogramming concepts: traits, type manipulation, type wrappers, and moreAn in-depth look at metafunctions and metafunction classesSequences, algorithms, iterators, diagnostics, views, iterator adaptors, and moreBoost MPL: motivation, usage, design, implementation, and practical examplesLessons and best practices for C++ template metaprogrammingCrossing the compile-time/runtime boundary Domain-Specific Embedded Languages, including a complete DSEL design walkthroughImproving compile-time performanceA Boost MPL case study in event handling