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

Learning about the ordering of templates with constraints

When a compiler encounters function calls or class template instantiations, it needs to figure out what overload (for a function) or specialization (for a class) is the best match. A function may be overloaded with different type constraints. Class templates can also be specialized with different type constraints. In order to decide which is the best match, the compiler needs to figure out which one is the most constrained and, at the same time, evaluates to true after substituting all the template parameters. In order to figure this out, it performs the constraints normalization. This is the process of transforming the constraint expression into conjunctions and disjunctions of atomic constraints, as described at the end of the previous section.

An atomic constraint A is said to subsume another atomic constraint B if A implies B. A constraint declaration D1 whose constraints subsume the constraints of another declaration...