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

Defining variable templates

Variable templates were introduced in C++14 and allow us to define variables that are templates either at namespace scope, in which case they represent a family of global variables, or at class scope, in which case they represent static data members.

A variable template is declared at a namespace scope as shown in the following code snippet. This is a typical example that you can find in the literature, but we can use it to elaborate on the benefits of variable templates:

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

The syntax is similar to declaring a variable (or data member) but combined with the syntax for declaring templates.

The question that arises is how variable templates are actually helpful. To answer this, let's build up an example to demonstrate the point. Let's consider we want to write a function template that, given the radius of a sphere, returns its volume. The volume of a sphere is 4πr...