Back to Basics Lambda Expressions Barbara Geller & Ansel Sermersheim CppCon September 2020Introduction ● Prologue ● History ● Function Pointer ● Function Object ● Definition of a Lambda Expression slot library ○ 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 memory ■ languages which were influenced by lambda calculus ● Haskell, LISP, and ML 5Lambda Expressions ● History ○ why do we use the terminology lambda expression ■ greek letter λ refers to an anonymous

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. . . . . . . . . . . . . . . . . . . . . . . . . 12 3 Basic Programming 15 3.1 Evaluating Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 3.2 Recursive Tactic Monad . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 5.2 Names and Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 5.3 Examples formal axiomatic framework in which one can define mathematical objects and reason about them. But expressions in Lean have a computational interpretation, which is to say, they can be evaluated. Any closed

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 3 Expressions 15 3.1 Errors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 3.9 Unit Expressions and Parenthesized Expressions . . . . . . . . . . . . . . . . . . . . . . . . 21 3.10 Arithmetic Sequences . . . . . . . . . . . . . . 21 3.12 Let Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 3.13 Case Expressions . . . . . . . . . . . . . . . . . . . .

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, and 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, and std::forward(self).m_name; }11 Explicit Object Parameters  Allows for recursive lambda expressions  this in a lambda accesses the object that contains the lambda, not the lambda instance itself

array constructor . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Dynamic array constant expressions . . . . . . . . . . . . . . . . . . . . . . 49 Packing and unpacking an array . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 3.7.2 Variants in assignments and expressions . . . . . . . . . . . . . . . . . . . . 62 3.7.3 Variants and interfaces . . . . . . . . . . 10Enumeration in Objective-C classes . . . . . . . . . . . . . . . . . . . . . . . . . . 167 12 Expressions 169 12.1 Expression syntax . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 4.1. Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3. Conditional Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 4.1.4. NULL in Expressions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 311 6.1.16. Common Table Expressions (“WITH … AS … SELECT”) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 312 6.2. INSERT

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50 4.1. Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1.3. Conditional Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 4.1.4. NULL in Expressions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 6.1.14. Common Table Expressions (“WITH … AS … SELECT”) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 6.2. INSERT

the language level. For example Jinja2 treats the non- breaking space as valid whitespace inside expressions which requires knowledge of the encoding or operating on an Unicode string. For more details about depending on if autoescaping is active or not. volatile True if the compiler cannot evaluate some expressions at compile time. At runtime this should always be False. 2.16 Custom Tests Tests work like filters even if you are not intercepting the call. Jinja2 might internally call the method to evaluate expressions. 43 44 CHAPTER 4 Native Python Types The default Environment renders templates to strings

/ namedtuples Returning Clause Common Table Expressions Foreign Keys and Joins Query operators Three valued logic Adding user-defined operators Expressions SQL Functions SQL Helper Security and SQL Injection 1960-01-15 # Herb 1950-05-05 # Grandma L. 1935-03-01 Combining filter expressions Peewee supports arbitrarily-nested expressions. Let’s get all the people whose birthday was either: before 1940 (grandma) an object is not found in the database. def get_object_or_404(model, *expressions): try: return model.get(*expressions) except model.DoesNotExist: abort(404) Note To avoid having