Book Image

Boost C++ Application Development Cookbook - Second Edition

By : Anton Polukhin Alekseevic
Book Image

Boost C++ Application Development Cookbook - Second Edition

By: Anton Polukhin Alekseevic

Overview of this book

If you want to take advantage of the real power of Boost and C++ and avoid the confusion about which library to use in which situation, then this book is for you. Beginning with the basics of Boost C++, you will move on to learn how the Boost libraries simplify application development. You will learn to convert data such as string to numbers, numbers to string, numbers to numbers and more. Managing resources will become a piece of cake. You’ll see what kind of work can be done at compile time and what Boost containers can do. You will learn everything for the development of high quality fast and portable applications. Write a program once and then you can use it on Linux, Windows, MacOS, Android operating systems. From manipulating images to graphs, directories, timers, files, networking – everyone will find an interesting topic. Be sure that knowledge from this book won’t get outdated, as more and more Boost libraries become part of the C++ Standard.
Table of Contents (19 chapters)
Title Page
Credits
About the Author
About the Reviewer
www.PacktPub.com
Customer Feedback
Preface

Making a higher-order metafunction


Functions that accept other functions as an input parameter or functions that return other functions are called higher-order functions. For example, the following functions are higher order:

typedef void(*function_t)(int);

function_t higher_order_function1();
void higher_order_function2(function_t f);
function_t higher_order_function3(function_t f); f); 

We already saw higher-order metafunctions in the recipes Using type vector of types and Manipulating vector of types recipes from this chapter, where we used boost::mpl::transform.

In this recipe, we'll try to make our own higher-order metafunction named coalesce, which accepts two types and two metafunctions. The coalesce metafunction applies the first type-parameter to the first metafunction and compares the resulting type with the boost::mpl::false_ type. If the resulting type is the boost::mpl::false_ type, it returns the result of applying the second type-parameter to the second metafunction, otherwise...