Alexandrescu Andrei - Modern C++ Design: Generic Programming and Design Patterns Applied

Generic Programming and Design Patterns Applied

Andrei Alexandrescu

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Library of Congress Cataloging-in-Publication Data
Alexandrescu, Andrei.
Modern C++ design : generic programming and design patterns applied /
Andrei Alexandrescu.
p. cm. (C++ in depth series)
Includes bibliographical references and index.
ISBN 0-201-70431-5
1. C++ (Computer program language) 2. Generic programming (Computer science)
I. Title. II. Series.
QA76.73.C153 A42 2001
005.133dc21 00-049596

Copyright 2001 by Addison-Wesley

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form, or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior consent of the publisher. Printed in the United States of America. Published simultaneously in Canada.

ISBN 0-201-70431-5

Text printed in the United States on recycled paper at RR Donnelley Crawfordsville in Crawfordsville, Indiana.

19th Printing January 2011

Bjarne Stroustrup, Editor

I have made this letter longer than usual, because I lack the time to make it short.

BLAISE PASCAL

The advent of the ISO/ANSI C++ standard marked the beginning of a new era for C++ programmers. The standard offers many new facilities and opportunities, but how can a real-world programmer find the time to discover the key nuggets of wisdom within this mass of information? The C++ In-Depth Series minimizes learning time and confusion by giving programmers concise, focused guides to specific topics.

Each book in this series presents a single topic, at a technical level appropriate to that topic. The Series practical approach is designed to lift professionals to their next level of programming skills. Written by experts in the field, these short, in-depth monographs can be read and referenced without the distraction of unrelated material. The books are cross-referenced within the Series, and also reference The C++ Programming Language by Bjarne Stroustrup.

As you develop your skills in C++, it becomes increasingly important to separate essential information from hype and glitz, and to find the in-depth content you need in order to grow. The C++ In-Depth Series provides the tools, concepts, techniques, and new approaches to C++ that will give you a critical edge.

Accelerated C++: Practical Programming by Example, Andrew Koenig and Barbara E. Moo

Applied C++: Practical Techniques for Building Better Software, Philip Romanik and Amy Muntz

The Boost Graph Library: User Guide and Reference Manual, Jeremy G. Siek, Lie-Quan Lee, and Andrew Lumsdaine

C++ Coding Standards: 101 Rules, Guidelines, and Best Practices, Herb Sutter and Andrei Alexandrescu

C++ In-Depth Box Set, Bjarne Stroustrup, Andrei Alexandrescu, Andrew Koenig, Barbara E. Moo, Stanley B. Lippman, and Herb Sutter

C++ Network Programming, Volume 1: Mastering Complexity with ACE and Patterns, Douglas C. Schmidt and Stephen D. Huston

C++ Network Programming, Volume 2: Systematic Reuse with ACE and Frameworks, Douglas C. Schmidt and Stephen D. Huston

C++ Template Metaprogramming: Concepts, Tools, and Techniques from Boost and Beyond, David Abrahams and Aleksey Gurtovoy

Essential C++, Stanley B. Lippman

Exceptional C++: 47 Engineering Puzzles, Programming Problems, and Solutions, Herb Sutter

Exceptional C++ Style: 40 New Engineering Puzzles, Programming Problems, and Solutions, Herb Sutter

Modern C++ Design: Generic Programming and Design Patterns Applied, Andrei Alexandrescu

More Exceptional C++: 40 New Engineering Puzzles, Programming Problems, and Solutions, Herb Sutter

For more information, check out the series web site at www.awprofessional.com/series/indepth/

In 1991, I wrote the first edition of Effective C++. The book contained almost no discussions of templates, because templates were such a recent addition to the language, I knew almost nothing about them. What little template code I included, I had verified by e-mailing it to other people, because none of the compilers to which I had access offered support for templates.

In 1995, I wrote More Effective C++. Again I wrote almost nothing about templates. What stopped me this time was neither a lack of knowledge of templates (my initial outline for the book included an entire chapter on the topic) nor shortcomings on the part of my compilers. Instead, it was a suspicion that the C++ communitys understanding of templates was about to undergo such dramatic change, anything I had to say about them would soon be considered trite, superficial, or just plain wrong.

There were two reasons for that suspicion. The first was a column by John Barton and Lee Nackman in the January 1995 C++ Report that described how templates could be used to perform typesafe dimensional analysis with zero runtime cost. This was a problem Id spent some time on myself, and I knew that many had searched for a solution, but none had succeeded. Barton and Nackmans revolutionary approach made me realize that templates were good for a lot more than just creating containers of T.

As an example of their design, consider this code for multiplying two physical quantities of arbitrary dimensional type:

template
Physical operator*(Physical lhs,
Physical rhs)
{
return Physical::unit*lhs.value()*rhs.value();
}

Even without the context of the column to clarify this code, its clear that this function template takes six parameters, none of which represents a type! This use of templates was such a revelation to me, I was positively giddy.

Shortly thereafter, I started reading about the STL. Alexander Stepanovs elegant library design, where containers know nothing about algorithms; algorithms know nothing about containers; iterators act like pointers (but may be objects instead); containers and algorithms accept function pointers and function objects with equal aplomb; and library clients may extend the library without having to inherit from any base classes or redefine any virtual functions, made me feelas I had when I read Barton and Nackmans worklike I knew almost nothing about templates.

So I wrote almost nothing about them in More Effective