Modern C++ Design: Generic Programming and Design Patterns Applied [Paperback]

You might be holding this book in a bookstore, asking yourself whether you should buy it. Or maybe you are in your employers library, wondering whether you should invest time in reading it. I know you dont have time, so Ill cut to the chase. If you have ever asked yourself how to write higher-level programs in C++, how to cope with the avalanche of irrelevant details that plague even the cleanest design, or how to build reusable components that you dont have to hack into each time you take them to your next application, then this book is for you.

Imagine the following scenario. You come from a design meeting with a couple of printed diagrams, scribbled with your annotations. Okay, the event type passed between these objects is not char anymore; its int. You change one line of code. The smart pointers to Widget are too slow; they should go unchecked. You change one line of code. The object factory needs to support the new Gadget class just added by another department. You change one line of code.

You changed the design. Compile. Link. Done.

Well, there is something wrong with this scenario, isnt there? A much more likely scenario is this: You come from the meeting in a hurry because you have a pile of work to do. You fire a global search. You perform surgery on code. You add code. You introduce bugs. You remove the bugs . . . thats the way a programmers job is, right? Although this book cannot possibly promise you the first scenario, it is nonetheless a resolute step in that direction. It tries to present C++ as a newly discovered language for software architects.

Traditionally, code is the most detailed and intricate aspect of a software system. Historically, in spite of various levels of language support for design methodologies (such as object orientation), a significant gap persisted between the blueprints of a program and its code because the code must take care of the ultimate details of the implementation and of many ancillary tasks. The intent of the design is, more often than not, dissolved in a sea of quirks.

This book presents a collection of reusable design artifacts, called generic components, together with the techniques that make them possible. These generic components bring their users the well-known benefits of libraries, but in the broader space of system architecture. The coding techniques and the implementations provided focus on tasks and issues that traditionally fall in the area of design, activities usually done before coding. Because of their high level, generic components make it possible to map intricate architectures to code in unusually expressive, terse, and easy-to-maintain ways.

Three elements are reunited here: design patterns, generic programming, and C++. These elements are combined to achieve a very high rate of reuse, both horizontally and vertically. On the horizontal dimension, a small amount of library code implements a combinatorialand essentially open-endednumber of structures and behaviors. On the vertical dimension, the generality of these components makes them applicable to a vast range of programs.

This book owes much to design patterns, powerful solutions to ever-recurring problems in object-oriented development. Design patterns are distilled pieces of good designrecipes for sound, reusable solutions to problems that can be encountered in manycontexts. Design patterns concentrate on providing a suggestive lexicon for designs to be conveyed. They describe the problem, a time-proven solution with its variants, and the consequences of choosing each variant of that solution. Design patterns go above and beyond anything a programming language, no matter how advanced, could possibly express. By following and combining certain design patterns, the components presented in this book tend to address a large category of concrete problems.

Generic programming is a paradigm that focuses on abstracting types to a narrow collection of functional requirements and on implementing algorithms in terms of these requirements. Because algorithms define a strict and narrow interface to the types they operate on, the same algorithm can be used against a wide collection of types. The implementations in this book use generic programming techniques to achieve a minimal commitment to specificity, extraordinary terseness, and efficiency that rivals carefully handcrafted code.

C++ is the only implementation tool used in this book. You will not find in this book code that implements nifty windowing systems, complex networking libraries, or clever logging mechanisms. Instead, you will find the fundamental components that make it easy to implement all of the above, and much more. C++ has the breadth necessary to make this possible. Its underlying C memory model ensures raw performance, its support for polymorphism enables object-oriented techniques, and its templates unleash an incredible code generation machine. Templates pervade all the code in the book because they allow close cooperation between the user and the library. The user of the library literally controls he way code is generated, in ways constrained by the library. The role of a generic component library is to allow user-specified types and behaviors to be combined with generic components in a sound design. Because of the static nature of the technique used, errors in mixing and matching the appropriate pieces are usually caught during compile time.

This books manifest intent is to create generic componentspreimplemented pieces of design whose main characteristics are flexibility, versatility, and ease of use. Generic components do not form a framework. In fact, their approach is complementarywhereas a framework defines interdependent classes to foster a specific object model, generic components are lightweight design artifacts that are independent of each other, yet can be mixed and matched freely. They can be of great help in implementing frameworks.

Audience

The intended audience of this book falls into two main categories. The first category is that of experienced C++ programmers who want to master the most modern library writing techniques. The book presents new, powerful C++ idioms that have surprising capabilities, some of which werent even thought possible. These idioms are of great help in writing high-level libraries. Intermediate C++ programmers who want to go a step further will certainly find the book useful, too, especially if they invest a bit of perseverance. Although pretty hard-core C++ code is sometimes presented, it is thoroughly explained.

The second category consists of busy programmers who need to get the job done without undergoing a steep learning investment. They can skim the most intricate details of implementation and concentrate on using the provided library. Each chapter has an introductory explanation and ends with a Quick Facts section. Programmers will find these features a useful reference in understanding and using the components. The components can be understood in isolation, are very powerful yet safe, and are a joy to use.

You need to have a solid working experience with C++ and, above all, the desire to learn more. A degree of familiarity with templates and the Standard Template Library (STL) is desirable.

Having an acquaintance with design patterns (Gamma et al. 1995) is recommended but not mandatory. The patterns and idioms applied in the book are described in detail. However, this book is not a pattern bookit does not attempt to treat patterns in full generality. Because patterns are presented from the pragmatic standpoint of a library writer, even readers interested mostly in patterns may find the perspective refreshing, if constrained.

Loki

The book describes an actual C++ library called Loki. Loki is the god of wit and mischief in Norse mythology, and the authors hope is that the librarys originality and flexibility will remind readers of the playful Norse god. All the elements of the library live in the namespace Loki. The namespace is not mentioned in the coding examples because it would have unnecessarily increased indentation and the size of the examples.This, alas, means that many current compilers cannot cope with parts of it. I implemented and tested Loki using Metrowerks CodeWarrior Pro 6.0 and Comeau C++ 4.2.38, both on Windows. It is likely that KAI C++ wouldnt have any problem with the code, either. As vendors release new, better compiler versions, you will be able to exploit everything Loki has to offer.

Lokis code and the code samples presented throughout the book use a popular coding standard originated by Herb Sutter. Im sure you will pick it up easily. In a nutshell,

Classes, functions, and enumerated types look LikeThis.

Variables and enumerated values look likeThis.

Member variables look likeThis_.

Template parameters are declared with class if they can be only a user-defined type, and with typename if they can also be a primitive type.

Organization

The book consists of two major parts: techniques and components. Part I (Chapters 1 to 4) describes the C++ techniques that are used in generic programming and in particular in building generic components. A host of C++-specific features and techniques are presented: policy-based design, partial template specialization, typelists, local classes, and more. You may want to read this part sequentially and return to specific sections for reference.

Part II builds on the foundation established in Part I by implementing a number of generic components. These are not toy examples; they are components of industrial strength used in real-world applications. Recurring issues that C++ developers face in their day-to-day activity, such as smart pointers, object factories, and functor objects, are discussed in depth and implemented in a generic way. The text presents implementations starting from the needs, the fundamental problems. Instead of explaining what a body of code does, the approach of the book is to discuss problems, take design decisions, and implement those decisions gradually.

Chapter 1 presents policiesa C++ idiom that helps in creating flexible designs.

Chapter 2 discusses general C++ techniques related to generic programming.

Chapter 3 implements typelists, which are powerful type manipulation structures.

Chapter 4 introduces an important ancillary tool: a small-object allocator.

Chapter 5 introduces the concept of generalized functors, useful in designs that use the Command design pattern.

Chapter 6 describes Singleton objects.

Chapter 7 discusses and implements smart pointers.

Chapter 8 describes generic object factories.

Chapter 9 treats the Abstract Factory design pattern and provides implementations of it.

Chapter 10 implements several variations of the Visitor design pattern in a generic manner.

Chapter 11 implements several multimethod engines, solutions that foster various trade-offs.

The design themes cover many important situations that C++ programmers have to cope with on a regular basis. I personally consider object factories (Chapter 8) a cornerstone of virtually any quality polymorphic design. Also, smart pointers (Chapter 7) are an important component of many C++ applications, small and large. Generalized functors (Chapter 5) have an incredibly broad range of applications. Once you have generalized functors, many complicated design problems become very simple. The other, more specialized, generic components, such as Visitor (Chapter 10) or multimethods (Chapter 11) have important niche applications and stretch the boundaries of language support.