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

Variadic class templates

Class templates may also have a variable number of template arguments. This is key to building some categories of types, such as tuple and variant, that are available in the standard library. In this section, we will see how we could write a simple implementation for a tuple class. A tuple is a type that represents a fixed-size collection of heterogeneous values.

When implementing variadic function templates we used a recursion pattern with two overloads, one for the general case and one for ending the recursion. The same approach has to be taken with variadic class templates, except that we need to use specialization for this purpose. Next, you can see a minimal implementation for a tuple:

template <typename T, typename... Ts>
struct tuple
   tuple(T const& t, Ts const &... ts)
      : value(t), rest(ts...)
   constexpr int size() const...