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

Using constexpr if

A C++17 feature makes SFINAE much easier. It’s called constexpr if and it’s a compile-time version of the if statement. It helps replace complex template code with simpler versions. Let’s start by looking at a C++17 implementation of the serialize function that can uniformly serialize both widgets and gadgets:

template <typename T>
void serialize(std::ostream& os, T const& value)
   if constexpr (uses_write_v<T>)
      os << value;

The syntax for constexpr if is if constexpr(condition). The condition must be a compile-time expression. There is no short-circuit logic performed when evaluating the expression. This means that if the expression has the form a && b or a || b, then both a and b must be well-formed.

constexpr if enables us to discard a branch, at compile-time, based on...