Template Metaprogramming: Type Traits Part 1 CppCon 2020 1 Jody Hagins
 jhagins@maystreet.com 
 coachhagins@gmail.comTemplate Metaprogramming: Type Traits CppCon 2020 2 IntroductionIntended Audience necessarily beginner to C++, but beginner to traditional template metaprogramming techniques • Type traits part of standard library for ~10 years 3Intended 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 3Intended

. . . . . . . . . . . 72 13 Methods and Traits 75 13.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 2 13.2 Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 13.2.1 Implementing Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 13.2.2 Supertraits . . . . . . . . . . . . . . . . . . . . . . . . . . . . Generic Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 15.3 Generic Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86 15.4 Trait Bounds . . .

. . . . . . . . . . . 68 13 Methods and Traits 71 13.1 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 2 13.2 Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 13.2.1 Implementing Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . 73 13.2.2 Supertraits . . . . . . . . . . . . . . . . . . . . . . . . . . . . Generic Data Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 15.3 Generic Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 15.4 Trait Bounds . . .

. 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

. . . . . . . . . . . . 72 13 Métodos y Traits 75 13.1 Métodos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 2 13.2 Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 13.2.1 Implementación de Traits . . . . . . . . . . . . . . . . . . . . . . . . 77 13.2.2 Supertraits . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tipos de datos asociados . . . . . . . . . . . . . . . . . . . . . . . . . 78 13.3 Derivación de Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79 13.4 Ejercicio: trait de registro

. . . . . . . . . . . . 72 13 Métodos e Traits 75 13.1 Métodos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 2 13.2 Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 13.2.1 Implementando Traits . . . . . . . . . . . . . . . . . . . . . . . . . . 77 13.2.2 Supertraits . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 15.2 Tipos de Dados Genéricos . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 15.3 Traits Genéricos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 15.4 Trait Bounds

whether monoid_traits specialization exists 117 using grb; bool test = is_monoid_v, int>; // Prints “1” for true std::cout << test << std::endl; int identity = monoid_traits whether monoid_traits specialization exists 118 using grb; bool test = is_monoid_v, int>; // Prints “1” for true std::cout << test << std::endl; int identity = monoid_traits whether monoid_traits specialization exists 119 using grb; bool test = is_monoid_v, int>; // Prints “1” for true std::cout << test << std::endl; int identity = monoid_traits

. . . . . . . . . . . . . . 78 2 13.2 Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 13.2.1 � � � � � � � � � Traits . . . . . . . . . . . . . . . . . . . . � � � � � � Generic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88 15.3 Generic Traits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 15.4 Trait Bounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 17 � � � � � � � � � � � � � � � � � Traits 102 17.1 � � � � � � . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

componentName: web-service instanceName: frontend dependencies: - backend traits: - trait: apiVersion: keda.k8s.io/v1alpha1 kind: ScaledObject com/oam-dev/spec EDAS的平台构建机制-KubeVela https://github.com/oam-dev/kubevela • OAM应用模型运行时 • 内置Workloads & Traits & Scopes • Capability Management KubeVela的核心机制-运行时 func Setup(mgr ctrl.Manager, args controller ParameterValues) w, err := r.workload.Render(c.Spec.Workload.Raw, p...) for _, ct := range acc.Traits { t, traitDef, err := r.renderTrait(ctx, ct, ac, acc.ComponentName, ref, dag) … } if err := Se

std::iterator_traits is not SFINAE-friendly until C++17 and requires all five typedefs to be defined until C++20３. To achieve C++20 behavior without modifying std::iterator_traits, iterators must used with pre-C++20 STL, which relies on std::iterator_traits. The opposite situation can be handled by specializing preview::incrementable_traits with pre- C++20 iterators５ such as std::back_insert_iterator std::back_insert_iterator, which are used to determine preview::iterator_traits::difference_type. Since stl-preview follows C++26 standard, it is self-consistent. Before C++17, where std::contiguous_iterator_tag