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

Learning more ways to specify constraints

We have discussed in this chapter about requires clauses and requires expressions. Although both are introduced with the new requires keyword, they are different things and should be fully understood:

  • A requires clause determines whether a function participates in overload resolution or not. This happens based on the value of a compile-time Boolean expression.
  • A requires expression determines whether a set of one or more expressions is well-formed, without having any side effects on the behavior of the program. A requires expression is a Boolean expression that can be used with a requires clause.

Let’s see an example again:

template <typename T>
concept addable = requires(T a, T b) { a + b; };
                       // [1] requires expression
template <typename T>
requires addable<T&gt...