Back to Basics Lambda Expressions Barbara Geller & Ansel Sermersheim CppCon September 2020Introduction ● Prologue ● History ● Function Pointer ● Function Object ● Definition of a Lambda Expression ● Capture Capture Clause ● Generalized Capture ● This ● Full Syntax as of C++20 ● What is the Big Deal ● Generic Lambda 2Prologue 3 ● Credentials ○ every library and application is open source ○ development using CsLibGuarded ■ library for managing access to data shared between threadsLambda Expressions ● History ○ lambda calculus is a branch of mathematics ■ introduced in the 1930’s to prove if “something” can be solved

Introduction The lambda trick Comparison Binding Constraints Architecture Substitution Construction Conclusion Symbolic Calculus for High-Performance Computing from Scratch using C++23 Vincent Reverdy Domain DedicationIntroduction The lambda trick Comparison Binding Constraints Architecture Substitution Construction Conclusion Table of contents 1 Introduction 2 The lambda trick 3 Comparison 4 Binding Domain DedicationIntroduction The lambda trick Comparison Binding Constraints Architecture Substitution Construction Conclusion Introduction 1 Introduction 2 The lambda trick 3 Comparison 4 Binding

Explicit Object Parameters  if consteval  Multidimensional Subscript Operator  Attributes on Lambda-Expressions  Literal Suffix for size_t  auto(x): decay-copy in The Language  #elifdef, #elifndef Explicit Object Parameters  if consteval  Multidimensional Subscript Operator  Attributes on Lambda-Expressions  Literal Suffix for size_t  auto(x): decay-copy in The Language  #elifdef, #elifndef Explicit Object Parameters  Allows for recursive lambda expressions  this in a lambda accesses the object that contains the lambda, not the lambda instance itself!  With deducing this: auto fibonacci

类型编译一遍，从而允许编译器更好 地进行自动适配与优化。 函数式编程： lambda 表达式 • C++11 引入的 lambda 表达式允许我们 在函数体内创建一个函数，大大地方便了 函数式编程。 • 语法就是先一个空的 [] ，然后是参数列表 ，然后是 {} 包裹的函数体。 • 再也不用被迫添加一个全局函数了！ lambda 表达式：返回类型 • lambda 表达式的返回类型写在参数列表 后面，用一个箭头 后面，用一个箭头 -> 表示。 lambda 表达式：自动推导返回类型 • 如果 lambda 表达式不通过 -> 指定类型 ，则和 -> auto 等价，自动根据函数体内 的 return 语句决定返回类型，如果没有 return 语句则相当于 -> void 。 lambda 表达式：捕获 main 中的变量 • lambda 函数体中，还可以使用定义他的 main 函数中的变量，只需要把方括号 函数可以引用定义位置所有的变量，这个 特性在函数式编程中称为闭包 (closure) 。 lambda 表达式：修改 main 中的变量 • [&] 不仅可以读取 main 中的变量，还可 以写入 main 中的变量，比如可以通过 counter++ 记录该函数被调用了多少次： lambda 表达式：传常引用避免拷贝开销 • 此外，最好把模板参数的 Func 声明为 Func const

unifex::task async_main<…>(span, auto&, auto&)::'lambda' at /home/cppcon/cppcon 7 : unifex::task async_main<…>(span, auto&, auto&)::'lambda' at /home/cppcon/cppcon 8 : unifex::task a unifex::task async_main<…>(span, auto&, auto&)::'lambda' at main.cpp:85 7 : unifex::task async_main<…>(span, auto&, auto&)::'lambda' at main.cpp:85 8 : unifex::task async_main<…>(span unifex::task async_main<…>(span, auto&, auto&)::'lambda' at main.cpp:85 7 : unifex::task async_main<…>(span, auto&, auto&)::'lambda' at main.cpp:85 8 : unifex::task async_main<…>(span

function (concepts & subsumption rules), you can add new overloads without touching old ones, • Lambda explicit template argument list is excellent! • Perfect forwarding may save you from writing multiple #define CPP2_FORCE_INLINE_LAMBDA [[msvc::forceinline]] #define CPP2_LAMBDA_NO_DISCARD #else #define CPP2_FORCE_INLINE __attribute__((always_inline)) #define CPP2_FORCE_INLINE_LAMBDA __attribute__((always_inline)) #define CPP2_LAMBDA_NO_DISCARD [[nodiscard]] #else #define CPP2_LAMBDA_NO_DISCARD #endif #elif defined(__GNUC__) #if __GNUC__ >= 9 #define CPP2_LAMBDA_NO_DISCARD [[nodiscard]] #else #define CPP2_LAMBDA_NO_DISCARD

lookup (mostly) this is still a pointer, not a reference (you can be sad) the meaning of this inside a lambda is unchangedYOU ALREADY KNOW HOW THIS WILL WORK We o�en think of the "this" parameter as the implicit A few things to cover here: this inside the lambda recursive lambdaMORE ON LAMBDAS A few things to cover here: this inside the lambda recursive lambda deriving from lambdas, overload setsMORE ON LAMBDAS LAMBDAS A few things to cover here: this inside the lambda recursive lambda deriving from lambdas, overload sets caveatsMORE ON LAMBDAS We must use language a bit carefully to distinguish between:MORE

. . . . . . . . . . . . . . . . . . . . . 36 Chapter 03: Language Runtime Enhancements 37 3.1 Lambda Expression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 Generic Lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 3.2 Function At the same time, a lot of enhancements have been made to the language runtime. The emergence of Lambda expressions has given C++ the “closure” feature of “anonymous functions”, which are in almost all

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 第 3 章语言运行期的强化 34 3.1 Lambda 表达式 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 基础 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 泛型 Lambda . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36 3.2 函数对象包装器 门，所有这些新标准中扩充的特性，给 C++ 这门语言注入了新的活力。那些还在坚持使用传统 C++ （本书把 C++98 及其之前的 C++ 特性均称之为传统 C++）而未接触过现代 C++ 的 C++ 程序员在 见到诸如 Lambda 表达式这类全新特性时，甚至会流露出『学的不是同一门语言』的惊叹之情。 现代 C++ (本书中均指 C++11/14/17/20) 为传统 C++ 注入的大量特性使得整个 C++ 变得更加 像一门现代化的语言。现代

monads, declarative syntax ○ C++ has all the tools to implement functional programming, including lambda functions, std::function, std::optional, std::expected, and more What is Functional Programming monads, declarative syntax ○ C++ has all the tools to implement functional programming, including lambda functions, std::function, std::optional, std::expected, and more ○ Want to maximize use of these monads, declarative syntax ○ C++ has all the tools to implement functional programming, including lambda functions, std::function, std::optional, std::expected, and more ○ Want to maximize use of these