The C# Type System

Title Page....7

Copyright....8

Dedication....9

About the Author and Technical Reviewer....10

Acknowledgments....11

Introduction....12

Who Should Read This Book....13

Organization and Requirements....13

Modern Features....15

Why Value Types?....15

1. Making the Most of the Type System....17

The Value of Good Names....17

Adding Clarity Through Types....19

Named Arguments....20

Custom Types....20

Encapsulation....21

Immutability....22

Value Validation....23

Testing....24

Refactoring....24

Replacing Magic Numbers with Named Constants....25

Simplifying Properties and Values....26

Overloading Arithmetic Operators....29

Determining a Need for New Types....30

Encoding Units....33

Itemizing Units with enums....33

Static Creation Methods....36

Symmetry in Design....38

Making Units Explicit....38

Choosing the Most Natural Usage....39

Returning Types Implied by Units....41

A Fully Formed Encapsulated Value....42

Deciding Whether to Abstract Types....42

Summary....43

2. Value and Reference Types....45

User-Defined Types....45

Structs and Classes....45

Records and Record Structs....46

Inheritance....47

Type Instance Lifetimes....49

Variables....50

Variables vs. Values....51

Definite Assignment....52

Instances and Storage....52

Embedded Values....52

Boxed Values....56

Semantics and Type....57

The Common Type System....57

Copy Semantics....58

Records, Structs, and Value Semantics....60

Construction and Initialization....61

Default Initialization....62

Instance Constructors....62

Field Initializers....69

Object Initializers....69

null Values and Default Values....71

Generics and null....72

Generics and Default Values....73

Nullable Value Types....74

Nullable Reference Types....75

The Null-Forgiving Operator....77

Summary....77

3. Reference and Value Parameters....79

Method Parameters and Arguments....79

Reference Types vs. By-Reference Parameters....80

Value Types and Parameters....81

The Value of a Reference....82

Reference Variables and Aliasing....83

Mutable By-Reference Parameters....85

Passing References by Reference....86

Passing Values by Reference....87

Working with Output Parameters....88

Limitations of By-Reference Parameters....91

Property Values....91

Overloading on By-Reference Parameters....92

Using Fields....93

Extension Methods....95

Side Effects and Direct Effects....97

Mutation vs. Creation....98

Declarative Code and Performance....100

Read-Only References and Returning by Reference....100

Returning Values by Reference....102

Preventing Modifications to Data....104

Keeping By-Reference Variables Within Scope....105

Considering Performance vs. Simplicity....109

Final Word on Mutable By-Reference Parameters....109

Summary....111

4. Implicit and Explicit Copying....112

Copying by Simple Assignment....112

Value Copy Behavior....113

Read-Only Properties vs. Immutable Types....115

Creating New Objects....116

Overwriting a Value....117

Constructing Value Types....118

Copying Records Like Value Types....120

Identifying Unnecessary Boxing....121

To an Interface....122

In Method Calls....123

Method Parameters and Arguments....124

Passing and Returning by Value....124

Accessing Properties....126

Using Expressions with Operators....127

Modifying Return Type Instances....129

Reference Type Properties....130

Instance Methods and Mutability....131

Properties as Arguments for Read-Only Parameters....132

Defensive Copies....133

Mutable Value Types and in Parameters....134

Automatic vs. Nonautomatic Properties....134

Read-Only Reference Variables....136

Read-Only Fields....137

Defending Against Mutation....138

Read-Only Accessors and Methods....138

Read-Only Types....139

Summary....140

5. Types of Equality....142

Built-in Equality....142

Whole Numbers....143

Floating-Point Values....144

Reference Equality....147

Strings and Value Equality....150

Custom Equality for Classes....151

Defining Equality Operators....152

Handling Comparisons with null....152

Making Type-Safe Comparisons....153

Working with Hash Codes....154

Structs and Equality....157

Overriding Equals for Structs....157

Boxing Values and Comparing by Identity....159

Comparing Generic Variables....163

Generic Code and the Equals Method....164

The IEquatable Interface....164

Compiler-Generated Equality....166

Records and Record Structs....166

Equality for Nullable Values....168

Value Tuples and Equality....170

Summary....172

6. The Nature of Values....174

Value vs. Reference Semantics....174

Copying and Equality Comparison Behavior....175

Mutability....179

Mechanics vs. Semantics....180

Object Relationships....181

Kinds of Objects....181

Object Characteristics....182

Design Refinement to Model Object Roles....188

Abstraction and Vocabulary....188

Encapsulation and Cohesion....189

Eliminating Duplication....190

Establishing Class Invariants....191

Clarifying with Symmetry....192

Encapsulation and the Public Interface....193

Extending the Interface....193

Reducing the Internal Interface....194

Composing Abstractions....195

Choosing Between Value and Reference Semantics....196

Avoiding the Pitfalls of Default Variables....196

Implementing Custom vs. Generated Behavior....197

Overriding Generated Methods....198

Comparison for Ordering....199

Equivalence vs. Equality....200

The Contract for Comparisons....201

Other Kinds of Ordering....201

The Perils of Uniformity and Consistency....203

Arithmetic and Nonarithmetic Types....203

Nonstandard Operator Behavior....204

Summary....205

7. Value Types and Polymorphism....206

Why Value Types Are Sealed....206

Implementation Inheritance....207

Value-Based Equality for Classes....208

Equality Behavior in Derived Classes....212

Equality Comparisons and Type Substitution....213

Inclusion Polymorphism and Subtyping....215

Working with Input and Output Types of Virtual Methods....216

Upholding a Type’s Contract....217

Inheriting Record Types....218

Avoiding Implementation Inheritance....223

Containing Instead of Inheriting Types....224

Parametric Polymorphism with Generics....225

Generic Constraints and Protocol Interfaces....226

Generic Method Parameters and Type Deduction....229

Parameterized Types....230

Ad Hoc Polymorphism with Overloading....231

Symbolic Polymorphism with Overloaded Operators....232

Generic Delegates for Polymorphism....233

Coercion Polymorphism Using Conversions....235

Widening vs. Narrowing Conversions....236

For Representation....236

For Purpose....237

Summary....239

8. Performance and Efficiency....241

Measuring and Optimizing Performance....241

The JIT Compiler....242

Performance Benchmarks....242

The Profiler....243

Measuring Basic Performance with Equals....244

Hidden Costs of Simplicity....246

The ValueType.Equals Method....247

The ValueType.GetHashCode Method....249

The HashCode.Combine Method....250

Optimizing Equality....251

The Effect of IEquatable....253

Property Accesses....254

The Equality Operators....255

How Type Affects Performance....259

Measuring the Cost of Copying....259

Copying Large Instances....260

Weighing Object Construction Costs....261

Measuring the Compiler-Generated Equals Method....264

How Common Idioms and Practices Affect Performance....266

Looping and Iteration....267

Pattern Matching and Selection....271

Summary....272

Afterword....274

Appendix: Further Reading....276

Index....287

The type system is the foundation upon which all C# programs are built. The C# Type System will show you how todefine and implement value types effectively, and write more performant and robust code. Real-world code examplesand test cases throughout will elevate your programming with C# and show you how best to implement the principlesyou’re learning.

Among the core aspects of working with the type system, you’ll learn:

• How user-defined value types, and even simple types, can enhance your code’s readability
• How reference and value types differ within C#
• How method parameters and arguments relate to reference and value types
• How differences in copy semantics between value and reference types affect a program’s behavior
• How the different methods of value comparisons for equality work behind the scenes
• The unique characteristics and roles of various types in an application, especially how value types go beyond meredata storage
• Why inheritance isn’t optimal for value types
• How to measure and evaluate the performance of an app’s use of different data types

Whether you’re a novice or seasoned programmer, you’ll find The C# Type System indispensable in your efforts to turngood code into great.