Jaakko Järvi Peter Dimov Douglas Gregor Dave Abrahams 1999 2000 Jaakko Järvi 2001 2002 Peter Dimov 2002 David 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. A utility library for passing references to generic functions

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>, two functions boost::ref and boost::cref that return instances of boost::reference_wrapper<T>, a function boost::unwrap_ref that unwraps a boost::reference_wrapper<T> or returns a reference to any other type of object, 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::unwrap_ref(x) returns a boost::unwrap_reference<X>::type& where X is the type of 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.

Contains a reference to an object of type T. reference_wrapper is primarily used to "feed" references to function templates (algorithms) that take their parameter by value. It provides an implicit conversion to T&, which usually allows the function templates to work on references unmodified. T T& Constructs a reference_wrapper object that stores a reference to t. Does not throw. T& The stored reference. Does not throw. T& The stored reference. Does not throw. T* A pointer to the object referenced by the stored reference. Does not throw. reference_wrapper<T> T& reference_wrapper<T>(t) Does not throw. reference_wrapper<T const> T const& reference_wrapper<T const>(t) Does not throw. unwrap_reference<T>::type& T& unwrap_reference<T>::type&(t) Does not throw. Determine if a type T is an instantiation of reference_wrapper. The value static constant will be true iff the type T is a specialization of reference_wrapper. bool unspecified Find the type in a reference_wrapper. The typedef type is T::type if T is a reference_wrapper, T otherwise. unspecified

ref and cref were originally part of the Tuple library by Jaakko Järvi. They were "promoted to boost:: status" by Peter Dimov because they are generally useful. Douglas Gregor and Dave Abrahams contributed is_reference_wrapper and unwrap_reference. Frank Mori Hess and Ronald Garcia contributed boost::unwrap_ref