CppCon 2020 Template Metaprogramming: Type Traits Part 1 Jody Hagins jhagins@maystreet.com coachhagins@gmail.com ## CppCon 2020 Template Metaprogramming: Type Traits Introduction ## I ntended Audience Not necessarily beginner to C++, but beginner to traditional template metaprogramming techniques • Type traits part of standard library for ~10 years ## I ntended Audience • Beginner/Intermediate • Gentle Not necessarily beginner to C++, but beginner to traditional template metaprogramming techniques • Type traits part of standard library for ~10 years • Fundamentals have been in use for ~20 years ## I

Literals 70 8.13 Annotated Strings 70 9 Functions 72 9.1 Argument Passing Behavior 73 9.2 Argument-type declarations 74 9.3 The return Keyword 75 9.4 Operators Are Functions 77 9.5 Operators With Special Types 127 12.1 Type Declarations 128 12.2 Abstract Types 130 12.3 Primitive Types 132 12.4 Composite Types 133 12.5 Mutable Composite Types 135 CONTENTS 12.6 Declared Types 136 12.7 Type Unions 137 12 9 UnionAll Types 146 12.10 Singleton types 147 12.11 Types of functions 148 12.12 Type{T} type selectors 149 12.13 Type Aliases 150 12.14 Operations on Types 151 12.15 Custom pretty-printing 152 12.16 “Value

Literals 69 8.13 Annotated Strings 70 9 Functions 72 9.1 Argument Passing Behavior 73 9.2 Argument-type declarations 74 9.3 The return Keyword 75 9.4 Operators Are Functions 77 9.5 Operators With Special Types 125 12.1 Type Declarations 126 12.2 Abstract Types 128 12.3 Primitive Types 129 12.4 Composite Types 130 12.5 Mutable Composite Types 132 CONTENTS 12.6 Declared Types 134 12.7 Type Unions 134 12 9 UnionAll Types 143 12.10 Singleton types 144 12.11 Types of functions 145 12.12 Type{T} type selectors 146 12.13 Type Aliases 148 12.14 Operations on Types 148 12.15 Custom pretty-printing 149 12.16 “Value

Functions ..... 81 15.1 Argument Passing Behavior ..... 82 15.2 The return Keyword ..... 82 Return type ..... 83 Returning nothing ..... 83 15.3 Operators Are Functions ..... 84 15.4 Operators With 116 Let Blocks ..... 120 For Loops and Comprehensions ..... 121 17.3 Constants ..... 122 18.1 Type Declarations ..... 126 18.2 Abstract Types ..... 127 18.3 Primitive Types ..... 129 18.4 Composite Composite Types ..... 129 18.5 Mutable Composite Types ..... 131 18.6 Declared Types ..... 132 18.7 Type Unions ..... 133 18.8 Parametric Types ..... 133 Parametric Composite Types ..... 134 Parametric

Literals ..... 61 8 Functions ..... 62 8.1 Argument Passing Behavior ..... 63 8.2 Argument-type declarations ..... 63 8.3 The return Keyword ..... 64 8.4 Operators Are Functions ..... 66 8 ..... 98 10.3 Constants ..... 108 10.4 typed Globals ..... 110 11 Types ..... 112 11.1 Type Declarations ..... 113 11.2 Abstract Types ..... 114 11.3 Primitive Types ..... 116 11.4 Composite 120 11.7 Type Unions ..... 121 11.8 Parametric Types ..... 121 11.9 UnionAll Types ..... 129 11.10 Singleton types ..... 131 11.11 Types of functions ..... 132 11.12 Type{T} type selectors

Literals ..... 64 8 Functions ..... 66 8.1 Argument Passing Behavior ..... 67 8.2 Argument-type declarations ..... 68 8.3 The return Keyword ..... 68 8.4 Operators Are Functions ..... 70 8 .... 105 10.3 Constants ..... 115 10.4 Typed Globals ..... 117 11 Types ..... 119 11.1 Type Declarations ..... 120 11.2 Abstract Types ..... 122 11.3 Primitive Types ..... 123 11.4 Composite 128 11.7 Type Unions ..... 128 11.8 Parametric Types ..... 129 11.9 UnionAll Types ..... 137 11.10 Singleton types ..... 138 11.11 Types of functions ..... 139 11.12 Type{T} type selectors

Literals ..... 64 8 Functions ..... 66 8.1 Argument Passing Behavior ..... 67 8.2 Argument-type declarations ..... 68 8.3 The return Keyword ..... 68 8.4 Operators Are Functions ..... 70 8 .... 105 10.3 Constants ..... 115 10.4 Typed Globals ..... 117 11 Types ..... 119 11.1 Type Declarations ..... 120 11.2 Abstract Types ..... 122 11.3 Primitive Types ..... 123 11.4 Composite 128 11.7 Type Unions ..... 128 11.8 Parametric Types ..... 129 11.9 UnionAll Types ..... 137 11.10 Singleton types ..... 138 11.11 Types of functions ..... 139 11.12 Type{T} type selectors

Literals 62 8 Functions 63 8.1 Argument Passing Behavior 64 8.2 The return Keyword 64 Return type 65 Returning nothing 65 8.3 Operators Are Functions 66 8.4 Operators With Special Names 66 Types 109 11.1 Type Declarations 110 11.2 Abstract Types 111 11.3 Primitive Types 113 11.4 Composite Types 114 11.5 Mutable Composite Types 116 11.6 Declared Types 116 11.7 Type Unions 117 Primitive Types 125 11.9 UnionAll Types 125 11.10 Singleton types 126 11.11 Type{T} type selectors 127 11.12 Type Aliases 128 11.13 Operations on Types 129 11.14 Custom pretty-printing 130

Literals 62 8 Functions 63 8.1 Argument Passing Behavior 64 8.2 The return Keyword 64 Return type 65 Returning nothing 65 8.3 Operators Are Functions 66 8.4 Operators With Special Names 66 Types 107 11.1 Type Declarations 108 11.2 Abstract Types 109 11.3 Primitive Types 111 11.4 Composite Types 112 11.5 Mutable Composite Types 114 11.6 Declared Types 114 11.7 Type Unions 115 Primitive Types 123 11.9 UnionAll Types 123 11.10 Singleton types 124 11.11 Type{T} type selectors 125 11.12 Type Aliases 126 11.13 Operations on Types 127 11.14 Custom pretty-printing 128

Literals 62 8 Functions 63 8.1 Argument Passing Behavior 64 8.2 The return Keyword 64 Return type 65 Returning nothing 65 8.3 Operators Are Functions 66 8.4 Operators With Special Names 66 Types 105 11.1 Type Declarations 106 11.2 Abstract Types 107 11.3 Primitive Types 109 11.4 Composite Types 110 11.5 Mutable Composite Types 112 11.6 Declared Types 112 11.7 Type Unions 113 Types 120 Singleton Types 121 Parametric Primitive Types 122 11.9 UnionAll Types 122 11.10 Type Aliases 123 11.11 Operations on Types 124 11.12 Custom pretty-printing 125 11.13 "Value