Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

Click here to view the latest version of this page.
PrevUpHomeNext

Chapter 14. Boost.Ref

Jaakko Järvi

Peter Dimov

Douglas Gregor

Dave Abrahams

Subject to the Boost Software License, Version 1.0. See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt.

Table of Contents

Introduction
Reference
Header <boost/ref.hpp>
Acknowledgements

Introduction

The Ref library is a small library that is useful for passing references to function templates (algorithms) that would usually take copies of their arguments. It defines the class template boost::reference_wrapper<T>, the two functions boost::ref and boost::cref that return instances of boost::reference_wrapper<T>, and the two traits classes boost::is_reference_wrapper<T> and boost::unwrap_reference<T>.

The purpose of boost::reference_wrapper<T> is to contain a reference to an object of type T. It is primarily used to "feed" references to function templates (algorithms) that take their parameter by value.

To support this usage, boost::reference_wrapper<T> provides an implicit conversion to T&. This usually allows the function templates to work on references unmodified.

boost::reference_wrapper<T> is both CopyConstructible and Assignable (ordinary references are not Assignable).

The expression boost::ref(x) returns a boost::reference_wrapper<X>(x) where X is the type of x. Similarly, boost::cref(x) returns a boost::reference_wrapper<X const>(x).

The expression boost::is_reference_wrapper<T>::value is true if T is a reference_wrapper, and false otherwise.

The type-expression boost::unwrap_reference<T>::type is T::type if T is a reference_wrapper, T otherwise.

Last revised: November 10, 2006 at 13:27:05 -0500


PrevUpHomeNext