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 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

documentation! Mypy is a static type checker for Python. Type checkers help ensure that you’re using variables and functions in your code correctly. With mypy, add type hints (PEP 484 [https://peps.python Unsupported operand types for + ("str" and "int") Adding type hints for mypy does not interfere with the way your program would otherwise run. Think of type hints as similar to comments! You can always use the means you can add type hints to your code base slowly and that you can always fall back to dynamic typing when static typing is not convenient. Mypy has a powerful and easy-to-use type system, supporting

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Type hints cheat sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 1.5 Type inference and type annotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.6 . . . . . . . . . . . . . . 55 1.11 Type narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 1.12 Duck type compatibility . . . . . . . . . . . .

documentation! Mypy is a static type checker for Python. Type checkers help ensure that you’re using variables and functions in your code correctly. With mypy, add type hints (PEP 484 [https://peps.python Unsupported operand types for + ("str" and "int") Adding type hints for mypy does not interfere with the way your program would otherwise run. Think of type hints as similar to comments! You can always use the means you can add type hints to your code base slowly and that you can always fall back to dynamic typing when static typing is not convenient. Mypy has a powerful and easy-to-use type system, supporting

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Type hints cheat sheet . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 1.5 Type inference and type annotations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.6 . . . . . . . . . . . . . . 54 1.11 Type narrowing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56 1.12 Duck type compatibility . . . . . . . . . . . .

Language Reference Abstract definitions Built-ins Coinduction Copatterns Core language Coverage Checking Cubical Cumulativity Data Types Flat Modality Foreign Function Interface Function Definitions Function Positivity Checking Postulates Pragmas Prop Record Types Reflection Rewriting Run-time Irrelevance Safe Agda Sized Types Sort System Syntactic Sugar Syntax Declarations Telescopes Termination Checking Universe page [https://github.com/agda/agda]. This is the manual for the Agda programming language, its type checking, compilation and editing system and related resources/tools. The latest PDF version of this manual

Language Reference Abstract definitions Built-ins Coinduction Copatterns Core language Coverage Checking Cubical Cumulativity Data Types Flat Modality Foreign Function Interface Function Definitions Function Positivity Checking Postulates Pragmas Prop Record Types Reflection Rewriting Run-time Irrelevance Safe Agda Sized Types Sort System Syntactic Sugar Syntax Declarations Telescopes Termination Checking Universe page [https://github.com/agda/agda]. This is the manual for the Agda programming language, its type checking, compilation and editing system and related resources/tools. The latest PDF version of this manual

Language Reference Abstract definitions Built-ins Coinduction Copatterns Core language Coverage Checking Cubical Cumulativity Data Types Flat Modality Foreign Function Interface Function Definitions Function Positivity Checking Postulates Pragmas Prop Record Types Reflection Rewriting Run-time Irrelevance Safe Agda Sized Types Sort System Syntactic Sugar Syntax Declarations Telescopes Termination Checking Universe page [https://github.com/agda/agda]. This is the manual for the Agda programming language, its type checking, compilation and editing system and related resources/tools. The latest PDF version of this manual

Language Reference Abstract definitions Built-ins Coinduction Copatterns Core language Coverage Checking Cubical Cubical compatible Cumulativity Data Types Flat Modality Foreign Function Interface Function Positivity Checking Postulates Pragmas Prop Record Types Reflection Rewriting Run-time Irrelevance Safe Agda Sized Types Sort System Syntactic Sugar Syntax Declarations Telescopes Termination Checking Two-Level Two-Level Type Theory Universe Levels With-Abstraction Without K Tools Automatic Proof Search (Auto) Command-line options Compilers Emacs Mode Literate Programming Generating HTML Generating LaTeX Interface

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45 3.6 Coverage Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 3.7 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 i 3.28 Positivity Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123 3.29 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 167 3.42 Termination Checking . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 168 3.43 Universe