Book Image

Template Metaprogramming with C++

By : Marius Bancila
Book Image

Template Metaprogramming with C++

By: Marius Bancila

Overview of this book

Learn how the metaprogramming technique enables you to create data structures and functions that allow computation to happen at compile time. With this book, you'll realize how templates help you avoid writing duplicate code and are key to creating generic libraries, such as the standard library or Boost, that can be used in a multitude of programs. The introductory chapters of this book will give you insights into the fundamentals of templates and metaprogramming. You'll then move on to practice writing complex templates and exploring advanced concepts such as template recursion, template argument deduction, forwarding references, type traits, and conditional compilation. Along the way, you'll learn how to write variadic templates and how to provide requirements to the template arguments with C++20 constraints and concepts. Finally, you'll apply your knowledge of C++ metaprogramming templates to implement various metaprogramming patterns and techniques. By the end of this book, you'll have learned how to write effective templates and implement metaprogramming in your everyday programming journey.
Table of Contents (16 chapters)
Part 1: Core Template Concepts
Part 2: Advanced Template Features
Part 3: Applied Templates
Appendix: Closing Notes

Chapter 6, Concepts and Constraints

Question 1

What are constraints? What about concepts?


A constraint is a requirement imposed on a template argument. A concept is a named set of one or more constraints.

Question 2

What is a requires clause and a requires expression?


A requires clause is a construct that allows us to specify a constraint on a template argument or function declaration. This construct is composed of the requires keyword followed by a compile-time Boolean expression. A requires clause affects the behavior of a function, including it for overload resolution only if the Boolean expression is true. On the other hand, a requires expression has the requires (parameters-list) expression; form, where parameters-list is optional. Its purpose is to verify that some expressions are well-formed, without having any side effects or affecting the behavior of the function. Requires expressions can be used with requires clauses, although named concepts...