C++ Software Design: Design Principles and Patterns for High-Quality Software

Preface....6

Why I Wrote This Book....6

What This Book Is About....7

Software Design....8

Modern C++....8

Design Patterns....9

Who This Book Is For....10

How This Book Is Structured....11

Conventions Used in This Book....12

Using Code Examples....13

O’Reilly Online Learning....14

How to Contact Us....14

Acknowledgments....15

1. The Art of Software Design....17

Guideline 1: Understand the Importance of Software Design....18

Features Are Not Software Design....18

Software Design: The Art of Managing Dependencies and Abstractions....19

The Three Levels of Software Development....22

The Focus on Features....27

The Focus on Software Design and Design Principles....29

Guideline 2: Design for Change....30

Separation of Concerns....30

An Example of Artificial Coupling....32

Logical Versus Physical Coupling....36

Don’t Repeat Yourself....41

Avoid Premature Separation of Concerns....46

Guideline 3: Separate Interfaces to Avoid Artificial Coupling....48

Segregate Interfaces to Separate Concerns....48

Minimizing Requirements of Template Arguments....51

Guideline 4: Design for Testability....53

How to Test a Private Member Function....54

The True Solution: Separate Concerns....59

Guideline 5: Design for Extension....63

The Open-Closed Principle....63

Compile-Time Extensibility....70

Avoid Premature Design for Extension....73

2. The Art of Building Abstractions....78

Guideline 6: Adhere to the Expected Behavior of Abstractions....79

An Example of Violating Expectations....79

The Liskov Substitution Principle....83

Criticism of the Liskov Substitution Principle....88

The Need for Good and Meaningful Abstractions....89

Guideline 7: Understand the Similarities Between Base Classes and Concepts....90

Guideline 8: Understand the Semantic Requirements of Overload Sets....95

The Power of Free Functions: A Compile-Time Abstraction Mechanism....96

The Problem of Free Functions: Expectations on the Behavior....99

Guideline 9: Pay Attention to the Ownership of Abstractions....103

The Dependency Inversion Principle....104

Dependency Inversion in a Plug-In Architecture....113

Dependency Inversion via Templates....118

Dependency Inversion via Overload Sets....119

Dependency Inversion Principle Versus Single-Responsibility Principle....122

Guideline 10: Consider Creating an Architectural Document....122

3. The Purpose of Design Patterns....130

Guideline 11: Understand the Purpose of Design Patterns....131

A Design Pattern Has a Name....131

A Design Pattern Carries an Intent....133

A Design Pattern Introduces an Abstraction....133

A Design Pattern Has Been Proven....137

Guideline 12: Beware of Design Pattern Misconceptions....138

Design Patterns Are Not a Goal....139

Design Patterns Are Not About Implementation Details....140

Design Patterns Are Not Limited to Object-Oriented Programming or Dynamic Polymorphism....144

Guideline 13: Design Patterns Are Everywhere....148

Guideline 14: Use a Design Pattern’s Name to Communicate Intent....154

4. The Visitor Design Pattern....160

Guideline 15: Design for the Addition of Types or Operations....161

A Procedural Solution....161

An Object-Oriented Solution....169

Be Aware of the Design Choice in Dynamic Polymorphism....172

Guideline 16: Use Visitor to Extend Operations....174

Analyzing the Design Issues....175

The Visitor Design Pattern Explained....177

Analyzing the Shortcomings of the Visitor Design Pattern....182

Guideline 17: Consider std::variant for Implementing Visitor....189

Introduction to std::variant....189

Refactoring the Drawing of Shapes as a Value-Based, Nonintrusive Solution....193

Performance Benchmarks....201

Analyzing the Shortcomings of the std::variant Solution....203

Guideline 18: Beware the Performance of Acyclic Visitor....205

5. The Strategy and Command Design Patterns....216

Guideline 19: Use Strategy to Isolate How Things Are Done....217

Analyzing the Design Issues....220

The Strategy Design Pattern Explained....227

Analyzing the Shortcomings of the Naive Solution....231

Comparison Between Visitor and Strategy....240

Analyzing the Shortcomings of the Strategy Design Pattern....241

Policy-Based Design....245

Guideline 20: Favor Composition over Inheritance....248

Guideline 21: Use Command to Isolate What Things Are Done....252

The Command Design Pattern Explained....252

The Command Design Pattern Versus the Strategy Design Pattern....262

Analyzing the Shortcomings of the Command Design Pattern....266

Guideline 22: Prefer Value Semantics over Reference Semantics....267

The Shortcomings of the GoF Style: Reference Semantics....268

Reference Semantics: A Second Example....272

The Modern C++ Philosophy: Value Semantics....275

Value Semantics: A Second Example....278

Prefer to Use Value Semantics to Implement Design Patterns....280

Guideline 23: Prefer a Value-Based Implementation of Strategy and Command....281

Introduction to std::function....281

Refactoring the Drawing of Shapes....284

Performance Benchmarks....292

Analyzing the Shortcomings of the std::function Solution....293

6. The Adapter, Observer, and CRTP Design Patterns....299

Guideline 24: Use Adapters to Standardize Interfaces....300

The Adapter Design Pattern Explained....301

Object Adapters Versus Class Adapters....304

Examples from the Standard Library....306

Comparison Between Adapter and Strategy....308

Function Adapters....309

Analyzing the Shortcomings of the Adapter Design Pattern....311

Guideline 25: Apply Observers as an Abstract Notification Mechanism....315

The Observer Design Pattern Explained....316

A Classic Observer Implementation....318

An Observer Implementation Based on Value Semantics....331

Analyzing the Shortcomings of the Observer Design Pattern....334

Guideline 26: Use CRTP to Introduce Static Type Categories....336

A Motivation for CRTP....337

The CRTP Design Pattern Explained....343

Analyzing the Shortcomings of the CRTP Design Pattern....351

The Future of CRTP: A Comparison Between CRTP and C++20 Concepts....355

Guideline 27: Use CRTP for Static Mixin Classes....358

A Strong Type Motivation....359

Using CRTP as an Implementation Pattern....362

7. The Bridge, Prototype, and External Polymorphism Design Patterns....370

Guideline 28: Build Bridges to Remove Physical Dependencies....371

A Motivating Example....371

The Bridge Design Pattern Explained....377

The Pimpl Idiom....382

Comparison Between Bridge and Strategy....387

Analyzing the Shortcomings of the Bridge Design Pattern....391

Guideline 29: Be Aware of Bridge Performance Gains and Losses....393

The Performance Impact of Bridges....394

Improving Performance with Partial Bridges....397

Guideline 30: Apply Prototype for Abstract Copy Operations....401

A Sheep-ish Example: Copying Animals....402

The Prototype Design Pattern Explained....404

Comparison Between Prototype and std::variant....410

Analyzing the Shortcomings of the Prototype Design Pattern....411

Guideline 31: Use External Polymorphism for Nonintrusive Runtime Polymorphism....412

The External Polymorphism Design Pattern Explained....413

Drawing of Shapes Revisited....417

Comparison Between External Polymorphism and Adapter....428

Analyzing the Shortcomings of the External Polymorphism Design Pattern....429

8. The Type Erasure Design Pattern....436

Guideline 32: Consider Replacing Inheritance Hierarchies with Type Erasure....437

The History of Type Erasure....438

The Type Erasure Design Pattern Explained....441

An Owning Type Erasure Implementation....445

Analyzing the Shortcomings of the Type Erasure Design Pattern....455

Comparing Two Type Erasure Wrappers....456

Interface Segregation of Type Erasure Wrappers....460

Performance Benchmarks....461

A Word About Terminology....463

Guideline 33: Be Aware of the Optimization Potential of Type Erasure....465

Small Buffer Optimization....465

Manual Implementation of Function Dispatch....477

Guideline 34: Be Aware of the Setup Costs of Owning Type Erasure Wrappers....484

The Setup Costs of an Owning Type Erasure Wrapper....485

A Simple Nonowning Type Erasure Implementation....488

A More Powerful Nonowning Type Erasure Implementation....491

9. The Decorator Design Pattern....505

Guideline 35: Use Decorators to Add Customization Hierarchically....506

Your Coworkers’ Design Issue....506

The Decorator Design Pattern Explained....515

A Classic Implementation of the Decorator Design Pattern....520

A Second Decorator Example....525

Comparison Between Decorator, Adapter, and Strategy....529

Analyzing the Shortcomings of the Decorator Design Pattern....531

Guideline 36: Understand the Trade-off Between Runtime and Compile Time Abstraction....534

A Value-Based Compile Time Decorator....535

A Value-Based Runtime Decorator....543

10. The Singleton Pattern....551

Guideline 37: Treat Singleton as an Implementation Pattern, Not a Design Pattern....552

The Singleton Pattern Explained....552

Singleton Does Not Manage or Reduce Dependencies....556

Guideline 38: Design Singletons for Change and Testability....558

Singletons Represent Global State....559

Singletons Impede Changeability and Testability....560

Inverting the Dependencies on a Singleton....567

Applying the Strategy Design Pattern....573

Moving Toward Local Dependency Injection....580

11. The Last Guideline....586

Guideline 39: Continue to Learn About Design Patterns....586

Index....591

Good software design is essential for the success of your project, but designing software is hard to do. You need to have a deep understanding of the consequences of design decisions and a good overview of available design alternatives. With this book, experienced C++ developers will get a thorough, practical, and unparalleled overview of software design with this modern language.

C++ trainer and consultant Klaus Iglberger explains how you can manage dependencies and abstractions, improve changeability and extensibility of software entities, and apply and implement modern design patterns to help you take advantage of today's possibilities. Software design is the most essential aspect of a software project because it impacts the software's most important properties: maintainability, changeability, and extensibility.

• Learn how to evaluate your code with respect to software design
• Understand what software design is, including design goals such as changeability and extensibility
• Explore the advantages and disadvantages of each design approach
• Learn how design patterns help solve problems and express intent
• Choose the right form of a design pattern to get the most out of its advantages