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)
1
Part 1: Core Template Concepts
5
Part 2: Advanced Template Features
9
Part 3: Applied Templates
Appendix: Closing Notes

Fold expressions

A fold expression is an expression involving a parameter pack that folds (or reduces) the elements of the parameter pack over a binary operator. To understand how this works, we will look at several examples. Earlier in this chapter, we implemented a variable function template called sum that returned the sum of all its supplied arguments. For convenience, we will show it again here:

template <typename T>
T sum(T a)
{
   return a;
}
template <typename T, typename... Args>
T sum(T a, Args... args)
{
   return a + sum(args...);
}

With fold expressions, this implementation that requires two overloads can be reduced to the following form:

template <typename... T>
int sum(T... args)
{
    return (... + args);
}

There is no need for overloaded functions anymore. The expression (... + args) represents the fold expression, which upon evaluation becomes ((((arg0 + arg1) + arg2) + … ) + argN...