Preface

In 1998 Dave had the privilege of attending a workshop in Generic Programming at Dagstuhl Castle in Germany. Near the end of the workshop, 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.

Dave and Aleksey