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

The Curiously Recurring Template Pattern

This pattern has a rather curious name: the Curiously Recurring Template Pattern, or CRTP for short. It’s called curious because it is rather odd and unintuitive. The pattern was first described (and its name coined) by James Coplien in a column in the C++ Report in 1995. This pattern is as follows:

  • There is a base class template that defines the (static) interface.
  • Derived classes are themselves the template argument for the base class template.
  • The member functions of the base class call member functions of its type template parameter (which are the derived classes).

Let’s see how the pattern implementation looks in practice. We will transform the previous example with game units into a version using the CRTP. The pattern implementation goes as follows:

template <typename T>
struct game_unit
   void attack()