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

Using concepts to constrain auto parameters

In Chapter 2, Template Fundamentals, we discussed generic lambdas, introduced in C++14, as well as lambda templates, introduced in C++20. A lambda that uses the auto specifier for at least one parameter is called a generic lambda. The function object generated by the compiler will have a templated call operator. Here is an example to refresh your memory:

auto lsum = [](auto a, auto b) {return a + b; };

The C++20 standard generalizes this feature for all functions. You can use the auto specifier in the function parameter list. This has the effect of transforming the function into a template function. Here is an example:

auto add(auto a, auto b)
   return a + b;

This is a function that takes two parameters and returns their sum (or to be more precise, the result of applying operator+ on the two values). Such a function using auto for function parameters is called an abbreviated function template. It is basically...