Design C gui (eng).pdf

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Foreword

I should begin by confessing that I do not consider myself a world-class API designer or software

engineer. I do, however, consider myself an expert researcher in the areas of computer graphics

and geometric modeling. It was in this line of work that I first met Martin at Pixar Animation

Studios.

As a graphics researcher I was accustomed to writing mathematically sophisticated papers. I was

also formally trained as a computer scientist at a major university and had written my share of code.

Armed with this background, when I was presented with the opportunity to lead a group of software

engineers working on a new generation of animation software for Pixar, I figured that it couldn’t be

any more difficult than research. After all, research is, by definition, the creation of the unknown,

whereas engineering is the implementation of well-understood subjects. I could not have been more

wrong.

I came to realize that software engineering was, without a doubt, the most difficult challenge

I had ever been presented with. After more years than I care to admit, I eventually gave up and went

back to graphics research.

I can’t tell you how much I would have benefitted from a book such as “API Design for C ++ .”

Many of the lessons we learned the hard way have been captured by Martin in this insightful,

easy-to-use book. Martin approaches the subject not from the perspective of an academic software

researcher (although he draws heavily from results and insights gained there), but from the perspec-

tive of an in-the-trenches software engineer and manager. He has experienced firsthand the importance

of good software design and has emerged as an articulate voice of what “good” means. In this book

he presents effective strategies for achieving that goal.

I particularly like that Martin is not focusing just on API design, but more broadly on software

life cycles, allowing him to cover topics such as versioning, strategies for backward compatibility,

and branching methodologies.

In short, this book should be of great value to those creating or managing software activities. It is

a comprehensive collection of best practices that have proven themselves time and time again.

Tony DeRose

Senior Scientist and Research Group Lead, Pixar Animation Studios

Preface

Writing large applications in C ++ is a complex and tricky business. However, designing reusable C ++

interfaces that are robust, stable, easy to use, and durable is even more difficult. The best way to suc-

ceed in this endeavor is to adhere to the tenets of good Application Programming Interface (API)

design.

An API presents a logical interface to a software component and hides the internal details

required to implement that component. It offers a high-level abstraction for a module and promotes

code reuse by allowing multiple applications to share the same functionality.

Modern software development has become highly dependent on APIs, from low-level application

frameworks to data format APIs and graphical user interface (GUI) frameworks. In fact, common

software engineering terms such as modular development, code reuse, componentization, dynamic

link library or DLL, software frameworks, distributed computing, and service-oriented architecture

all imply the need for strong API design skills.

Some popular C and C ++ APIs that you may already be aware of include the Standard Template

Library (STL), Boost, the Microsoft Windows API (Win32), Microsoft Foundation Classes (MFC),

libtiff, libpng, zlib, libxml ++ ,OpenGL,MySQL ++ , Trolltech’s Qt, wxWidgets, GTK + , KDE, Sky-

peKit, POSIX pthreads, Intel’s Threading Building Blocks, the Netscape Plugin API, and the

Apache module API. In addition, many of Google’s open-source projects are C ++ ,asismuchof

thecodeonthe sourceforge.net , bitbucket.org ,and freshmeat.net Web sites.

APIs such as these are used in all facets of software development, from desktop applications, to

mobile computing and embedded systems, to Web development. For example, the Mozilla Firefox

Web browser is built on top of more than 80 dynamic libraries, each of which provides the imple-

mentation for one or more APIs.

Elegant and robust API design is therefore a critical aspect of contemporary software develop-

ment. One important way in which this differs from standard application development is the far

greater need for change management. As we all know, change is an inevitable factor in software

development; new requirements, feature requests, and bug fixes cause software to evolve in ways

that were never anticipated when it was first devised. However, changes to an API that is shared

by hundreds of end-user applications can cause major upheaval and ultimately may cause clients

to abandon an API. The primary goal of good API design is therefore to provide your clients with the

functionality they need while also causing minimal impact to their code

ideally zero impact when

you release a new version.

WHY YOU SHOULD READ THIS BOOK

If you write C ++ code that another engineer relies upon, you’re an API designer and this book has

been written for you.

Interfaces are the most important code that you write because a problem with your interface is far

more costly to fix than a bug in your implementation. For instance, an interface change may require

all of the applications based on your code to be updated, whereas an implementation-only change

can be integrated transparently and effortlessly into client applications when they adopt the new

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