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 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 entry: 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 ntended

rewrite of Yii, adopting the latest technologies and protocols, including Composer, PSR, namespaces, traits, and so forth. Version 2.0 represents the current generation of the framework and will receive the framework. Yii 2.0 also makes use of the latest features of PHP, such as namespaces $ ^{2} $ and traits $ ^{3} $ . Understanding these concepts will help you more easily pick up Yii 2.0. #### 1.2 Upgrading classes and interfaces $ ^{7} $ . • Late Static Bindings $ ^{8} $ . • Date and Time $ ^{9} $ . • Traits $ ^{10} $ • intl $ ^{11} $ . Yii 2.0 makes use of the intl PHP extension to support internationalization

. . 196 3.3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 206 4 Generic Types, Traits, and Lifetimes 213 4.1 Removing Duplication by Extracting a Function . . . . 214 4.2 . . . . . . generators implement, and this trait must be in scope for us to use those methods. Chapter 10 will cover traits in detail. Also, we’re adding two more lines in the middle. The rand:: thread_rng function will give upper bound, so we need to specify 1 and 101 to request a number between 1 and 100. Knowing which traits to use and which functions and methods to call from a crate isn’t something that you’ll just know

Evaluation ..... 69 12.5.1 Solution ..... 72 13 Methods and Traits ..... 75 13.1 Methods ..... 75 13.2 Traits 77 13.2.1 Implementing Traits 77 13.2.2 Supertraits 78 13.2.3 Associated Types 78 13 Back 83 15 Generics 84 15.1 Generic Functions 84 15.2 Generic Data Types 85 15.3 Generic Traits 86 15.4 Trait Bounds 86 15.5 impl Trait 87 15.6 dyn Trait 88 15.7 Exercise: Generic min 89 Vec 94 16.7 HashMap 95 16.8 Exercise: Counter 96 16.8.1 Solution 97 17 Standard Library Traits 99 17.1 Comparisons 99 17.2 Operators 100 17.3 From and Into 101 17.4 Casting 102 17.5

Evaluation ..... 66 12.5.1 Solution ..... 68 13 Methods and Traits ..... 71 13.1 Methods ..... 71 13.2 Traits 73 13.2.1 Implementing Traits 73 13.2.2 Supertraits 74 13.2.3 Associated Types 74 13 Back 79 15 Generics 80 15.1 Generic Functions 80 15.2 Generic Data Types 81 15.3 Generic Traits 81 15.4 Trait Bounds 82 15.5 impl Trait 83 15.6 dyn Trait 84 15.7 Exercise: Generic min 85 Vec 90 16.7 HashMap 91 16.8 Exercise: Counter 92 16.8.1 Solution 94 17 Standard Library Traits 95 17.1 Comparisons 95 17.2 Operators 96 17.3 From and Into 97 17.4 Casting 98 17.5 Read

.... 70 12.5.1 Solución ..... 72 13 Métodos y Traits ..... 75 13.1 Métodos ..... 75 13.2 Traits ..... 77 13.2.1 Implementación de Traits ..... 77 13.2.2 Supertraits ..... 78 13.2.3 Tipos Tipos de datos asociados ..... 78 13.3 Derivación de Traits ..... 79 13.4 Ejercicio: trait de registro ..... 79 13.4.1 Solución ..... 80 IV Día 2: tarde ..... 82 14 Te damos la bienvenida ... Genéricos ..... 84 15.1 Funciones genéricas ..... 84 15.2 Tipos de Datos Genéricos ..... 85 15.3 Traits Genéricos ..... 85 15.4 Trait Bounds ..... 86 15.5 impl Trait ..... 87 15.6 dyn Trait ....

容器全家桶及其妙用举例 5. 函子 functor 与 lambda 表达式知多少 6. 通过实战案例来学习 STL 算法库 7. C++ 标准输入输出流 & 字符串格式化 8. traits 技术，用户自定义迭代器与算法 9. allocator，内存管理与对象生命周期 ## ASCII 码 第1章 ## 计算机如何表达字符 USASCII code chart |B|D|B|D|B|D|B|D| short <= int <= long <= long long 即可）。 ## 关于 char 类型的一个冷知识 #include #include traits> int main() { if (std::is_signed::value) { printf("你的 char 是有符号的，我猜你是 x86 return 0; } bate@archer ~/Codes/course/15 (master) $ 你的 char 是有符号的，我猜你是 x86 架构traits> ## C 语言中的字符串 • 字符串 (string) 就是由字符 (character) 组成的数组。 • C 语言中，字符串用双引号 “” 包裹，字符用单引号 “” 包裹。

Expressões ..... 70 12.5.1 Solução ..... 72 13 Métodos e Traits ..... 75 13.1 Métodos ..... 75 13.2 Traits ..... 77 13.2.1 Implementando Traits ..... 77 13.2.2 Supertraits ..... 78 13.2.3 Tipos Associados (Generics) ..... 84 15.1 Funções Genéricas ..... 84 15.2 Tipos de Dados Genéricos ..... 85 15.3 Traits Genéricos ..... 85 15.4 Trait Bounds (Limites de Trait) ..... 86 15.5 impl Trait ..... 87 15 94 16.7 HashMap ..... 95 16.8 Exercício: Contador ..... 96 16.8.1 Solução ..... 98 17 Traits da Biblioteca Padrão ..... 99 17.1 Comparações ..... 99 17.2 Operadores ..... 100 17.3 From

CONDITIONS AT COMPILE TIME PRE C++20 ## PART III: CONDITIONS AT COMPILE TIME PRE C++20 traits>: • type_traits are part of library. • Verified at compile time. • A class type trait (since C++11): function. • Identifies a situation.traits> ## PART III: CONDITIONS AT COMPILE TIME PRE C++20 ## traits>: overview ## • Classes: • Queries • Helper classes (is constant) Arrays (remove_extent, remove_all_extent) • Transformation related functionality • Operations on traits (conjunction, disjunction, negation) ## Functions (C++20): • Member relationships (is_corresponding_member