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

Constraining non-template member functions

Non-template functions that are members of class templates can be constrained in a similar way to what we have seen so far. This enables template classes to define member functions only for types that satisfy some requirements. In the following example, the equality operator is constrained:

template <typename T>
struct wrapper
   T value;
   bool operator==(std::string_view str)
   requires std::is_convertible_v<T, std::string_view>
      return value == str;

The wrapper class holds a value of a T type and defines the operator== member only for types that are convertible to std::string_view. Let’s see how this can be used:

wrapper<int>         a{ 42 };
wrapper<char const*> b{ "42" };
if(a == 42)   {} // error