Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries

by Krzysztof Cwalina, Jeremy Barton, Brad Abrams

Overview

Master Today’s Best Practices for Building Reusable .NET Frameworks, Libraries, and Components

“.NET Core [contains] advances important to cloud application developers: performance, resource utilization, container support, and others. This third edition of Framework Design Guidelines adds guidelines related to changes that the .NET team adopted during transition from the world of client-server application to the world of the Cloud.”
—From the Foreword by Scott Guthrie

Framework Design Guidelines has long been the definitive guide to best practices for developing components and component libraries in Microsoft .NET. Now, this third edition has been fully revised to reflect game-changing API design innovations introduced by Microsoft through eight recent updates to C#, eleven updates to .NET Framework, and the emergence and evolution of .NET Core.

Three leading .NET architects share the same guidance Microsoft teams are using to evolve .NET, so you can design well-performing components that feel like natural extensions to the platform. Building on the book’s proven explanatory style, the authors and expert annotators offer insider guidance on new .NET and C# concepts, including major advances in asynchronous programming and lightweight memory access. Throughout, they clarify and refresh existing content, helping you take full advantage of best practices based on C# 8, .NET Framework 4.8, and .NET Core.

• Discover which practices should always, generally, rarely, or never be used—including practices that are no longer recommended
• Learn the general philosophy and fundamental principles of modern framework design
• Explore common framework design patterns with up-to-date C# examples
• Apply best practices for naming, types, extensibility, and exceptions
• Learn how to design libraries that scale in the cloud
• Master new async programming techniques utilizing Task and ValueTask
• Make the most of the Memory<T> and Span<T> types for lightweight memory access

This guide is an indispensable resource for everyone who builds reusable .NET-based frameworks, libraries, or components at any scale: large system frameworks, medium-size reusable layers of large distributed systems, extensions to system frameworks, or even small shared components.

Register your book for convenient access to downloads, updates, and/or corrections as they become available. See inside book for details.

Product Details

ISBN-13:	9780135896327
Publisher:	Pearson Education
Publication date:	06/01/2020
Series:	Addison-Wesley Microsoft Technology Series
Sold by:	Barnes & Noble
Format:	eBook
Pages:	624
Sales rank:	297,860
File size:	31 MB
Note:	This product may take a few minutes to download.
Age Range:	18 Years

About the Author

Krzysztof Cwalina is a Principal Architect at Microsoft. He was a founding member of the .NET Framework team, and throughout his career has designed many .NET Framework, .NET Core, and other APIs. He is currently working on Azure SDK APIs. Krzysztof graduated with BS and MS in computer science from the University of Iowa. 
Jeremy Barton is a Principal Software Engineer at Microsoft. The majority of his career in computer software has been on the design and development of shared libraries. Since 2005 his primary programming language is C#, and he joined the .NET Base Class Libraries team in 2015 and is primarily responsible for .NET Cryptography. Jeremy graduated from Rose-Hulman Institute of Technology with a BS in Computer Science and Discrete Mathematics. Since graduation, he has gotten a cat, married, and a pilot’s license.
Brad Abrams was a founding member of the Common Language Runtime and .NET Framework teams at Microsoft Corporation. He has been designing parts of the .NET Framework since 1998 and is currently a Group Program Manager at Google. Brad started his framework design career building the Base Class Library (BCL) that ships as a core part of the .NET Framework. Brad was also the lead editor on the Common Language Specification (CLS), the .NET Framework Design Guidelines, and the libraries in the ECMA/ISO CLI Standard. Brad has authored and coauthored multiple publications, including Programming in the .NET Environment and .NET Framework Standard Library Annotated Reference, Volumes 1 and 2. Brad graduated from North Carolina State University with a BS in computer science. You can find his most recent musings on his blog at http://blogs.msdn.com/BradA.

Read an Excerpt

This book, Framework Design Guidelines, presents best practices for designing frameworks, which are reusable object-oriented libraries. The guidelines are applicable to frameworks ranging in size and in their scale of reuse:

• Large system frameworks, such as the .NET Framework, usually consisting of thousands of types and used by millions of developers.
• Medium-size reusable layers of large distributed applications
• or extensions to system frameworks, such as the Web Services
• Enhancements.
• Small components shared among several applications; for example, a grid control library.

It is worth noting that this book focuses on design issues that directly affect the programmability of a framework (publicly accessible APIs). As a result, we generally do not cover much in terms of implementation details. Just like a user interface design book doesn't cover the details of how to implement hit testing, this book does not describe how to implement a binary sort, for example. This scope allows us to provide a definitive guide for framework designers instead of being yet another book about programming.

These guidelines were created in the early days of .NET Framework development. They started as a small set of naming and design conventions but have been enhanced, scrutinized, and refined to a point where they are generally considered the canonical way to design frameworks at Microsoft. They carry the experience and cumulative wisdom of thousands of developer hours over three versions of the .NET Framework. We tried to avoid basing the text purely on some idealistic design philosophies, and we think its day-to-day use by development teams at Microsoft has made it an intensely pragmatic book.

The book contains many annotations that explain trade-offs, explain history, amplify, or provide critiquing views on the guidelines. These annotations are written by experienced framework designers, industry experts, and users. They are the stories from the trenches that add color and setting for many of the guidelines presented.

To make them more easily distinguished in text, namespace names, classes, interfaces, methods, properties, and types are set in monospace font. The book assumes basic familiarity with .NET Framework programming. A few guidelines assume familiarity with features introduced in version 2.0 of the Framework. If you are looking for a good introduction to Framework programming, there are some excellent suggestions in the Suggested Reading List at the end of the book.

Guideline Presentation

The guidelines are organized as simple recommendations using Do, Consider, Avoid, and Do not. Each guideline describes either a good or bad practice and all have a consistent presentation. Good practices have a check mark in front of them, and bad practices have an X in front of them. The wording of each guideline also indicates how strong the recommendation is. For example, a Do guideline is one that should always¹ be followed (all examples are from this book):

DO name custom attribute classes with the suffix "Attribute."

public class ObsoleteAttribute : Attribute { ... }

On the other hand, Consider guidelines should generally be followed, but if you fully understand the reasoning behind a guideline and have a good reason to not follow it anyway, you should not feel bad about breaking the rules:

CONSIDER defining a struct instead of a class if instances of the type are small and commonly short-lived or are commonly embedded in other objects.

Similarly, Do not guidelines indicate something you should almost never do:

DO NOT assign instances of mutable types to read-only fields.

Less strong, Avoid guidelines indicate that something is generally not a good idea, but there are known cases where breaking the rule makes sense:

AVOID using

ICollection<T> or

ICollection as a parameter just to access the Count property.

Some more complex guidelines are followed with additional background information, illustrative code samples, and rationale:

DO implement

IEquatable<T> on value types. The

Object.Equals method on value types causes boxing and its default implementation is not very efficient because it uses reflection.

IEquatable<T>.Equals can offer much better performance and can be implemented so it does not cause boxing.

public struct Int32 : IEquatable{
public bool Equals(Int32 other){ ... }
}

Language Choice and Code Examples

One of the goals of the Common Language Runtime is to support a variety of programming languages: those provided by Microsoft, such as C++, VB, and C#, as well as third-party languages such as Eiffel, COBOL, Python, and others. Therefore, this book was written to be applicable to a broad set of languages that can be used to develop and consume modern frameworks. To reinforce the message of multilanguage framework design, we considered writing code examples using several different programming languages. However, we decided against this. We felt that using different languages would help to carry the philosophical message, but it could force readers to learn several new languages, which is not the objective of this book.

We decided to choose a single language that is most likely to be readable to the broadest range of developers. We picked C#, because it is a simple language from the C family of languages (C, C++, Java, and C#), a family with a rich history in framework development.

Choice of language is close to the hearts of many developers, and we offer apologies to those who are uncomfortable with our choice.

About This Book This book offers guidelines for framework design from the top down.

Chapter 1 is a brief introduction to the book, describing the general philosophy of framework design. This is the only chapter without guidelines.

Chapter 2, "Framework Design Fundamentals," offers principles and guidelines that are fundamental to overall framework design.

Chapter 3, "Naming Guidelines," contains naming guidelines for various parts of a framework, such as namespaces, types, members, and common design idioms.

Chapter 4, "Type Design Guidelines," provides guidelines for the general design of types.

Chapter 5,"Member Design," takes it a step further and presents guidelines for the design of members of types. Chapter 6, "Designing for Extensibility," presents issues and guidelines that are important to ensure appropriate extensibility in your framework.

Chapter 7, "Exceptions," presents guidelines for working with exceptions, the preferred error reporting mechanisms.

Chapter 8, "Usage Guidelines," contains guidelines for extending and using types that commonly appear in frameworks.

Chapter 9, "Common Design Patterns," offers guidelines and examples of common framework design patterns.

Appendix A contains a short description of coding conventions used in this book. Appendix B describes a tool called FxCop. The tool can be used to analyze framework binaries for compliance with the guidelines described in this book. A link to the tool is included on the DVD that accompanies this book.

Appendix C is an example of an API specification that framework designers within Microsoft create when designing APIs.

Included with the book is a DVD that contains several hours of video presentations covering topics presented in this book by the authors, a sample API specification, and other useful resources.

1.Always might be a bit too strong a word. There are guidelines that should literally be always followed, but they are extremely rare. On the other hand, you probably need to have a really unusual case for breaking a "Do" guideline and still have it be beneficial to the users of the framework.

Table of Contents

Figures xvii
Tables xix
Foreword to the Third Edition xxi
Foreword to the Second Edition xxiii
Foreword to the First Edition xxv
Preface xxvii
Acknowledgments xxxiii
About the Authors xxxv
About the Annotators xxxvii

Chapter 1: Introduction 1
1.1 Qualities of a Well-Designed Framework 3

Chapter 2: Framework Design Fundamentals 9
2.1 Progressive Frameworks 12
2.2 Fundamental Principles of Framework Design 15

Chapter 3: Naming Guidelines 41
3.1 Capitalization Conventions 42
3.2 General Naming Conventions 52
3.3 Names of Assemblies, DLLs, and Packages 61
3.4 Names of Namespaces 63
3.5 Names of Classes, Structs, and Interfaces 67
3.6 Names of Type Members 74
3.7 Naming Parameters 79
3.8 Naming Resources 81

Chapter 4: Type Design Guidelines 83
4.1 Types and Namespaces 85
4.2 Choosing Between Class and Struct 89
4.3 Choosing Between Class and Interface 92
4.4 Abstract Class Design 100
4.5 Static Class Design 102
4.6 Interface Design 104
4.7 Struct Design 106
4.8 Enum Design 111
4.9 Nested Types 124
4.10 Types and Assembly Metadata 127
4.11 Strongly Typed Strings 129

Chapter 5: Member Design 135
5.1 General Member Design Guidelines 135
5.2 Property Design 158
5.3 Constructor Design 165
5.4 Event Design 175
5.5 Field Design 180
5.6 Extension Methods 184
5.7 Operator Overloads 192
5.8 Parameter Design 202
5.9 Using Tuples in Member Signatures 220

Chapter 6: Designing for Extensibility 227
6.1 Extensibility Mechanisms 227
6.2 Base Classes 242
6.3 Sealing 244

Chapter 7: Exceptions 249
7.1 Exception Throwing 254
7.2 Choosing the Right Type of Exception to Throw 260
7.3 Using Standard Exception Types 273
7.4 Designing Custom Exceptions 279
7.5 Exceptions and Performance 281

Chapter 8: Usage Guidelines 287
8.1 Arrays 287
8.2 Attributes 291
8.3 Collections 294
8.4 DateTime and DateTimeOffset 306
8.5 ICloneable 308
8.6 IComparable<T> and IEquatable<T> 309
8.7 IDisposable 311
8.8 Nullable<T> 311
8.9 Object 312
8.10 Serialization 319
8.11 Uri 321
8.12 System.Xml Usage 323
8.13 Equality Operators 324

Chapter 9: Common Design Patterns 329
9.1 Aggregate Components 329
9.2 The Async Patterns 339
9.3 Dependency Properties 365
9.4 Dispose Pattern 372
9.5 Factories 394
9.6 LINQ Support 400
9.7 Optional Feature Pattern 408
9.8 Covariance and Contravariance 412
9.9 Template Method 423
9.10 Timeouts 426
9.11 XAML Readable Types 427
9.12 Operating on Buffers 430
9.13 And in the End... 464

Appendix A: C# Coding Style Conventions 465
A.1 General Style Conventions 466
A.2 Naming Conventions 480
A.3 Comments 482
A.4 File Organization 483

Appendix B: Obsolete Guidance 487

Appendix C: Sample API Specification 523

Appendix D: Breaking Changes 529
D.1 Modifying Assemblies 530
D.2 Adding Namespaces 531
D.3 Modifying Namespaces 532
D.4 Moving Types 532
D.5 Removing Types 533
D.6 Modifying Types 534
D.7 Adding Members 539
D.8 Moving Members 541
D.9 Removing Members 542
D.10 Overloading Members 544
D.11 Changing Member Signatures 545
D.12 Changing Behavior 553
D.13 A Final Note 556

Glossary 557
Index 563