Book Image

Template Metaprogramming with C++

By : Marius Bancila
5 (1)
Book Image

Template Metaprogramming with C++

5 (1)
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

Constraining variable templates and template aliases

As you well know, apart from function templates and class templates we also have variable templates and alias templates in C++. These make no exception of the need to define constraints. The same rules for constraining the template arguments discussed so far apply to these two. In this section, we will demonstrate them shortly. Let’s start with variable templates.

It is a typical example to define the PI constant for showing how variable templates work. Indeed, it is a simple definition that looks as follows:

template <typename T>
constexpr T PI = T(3.1415926535897932385L);

However, this only makes sense for floating-point types (and maybe other types such as decimal, which does not exist in C++ yet). Therefore, this definition should be restricted to floating-point types, as follows:

template <std::floating_point T>
constexpr T PI = T(3.1415926535897932385L);
std::cout << PI<double> &lt...