- ref.hpp- |
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- The header boost/ref.hpp 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. -
-
-namespace boost
-{
- template<class T> class reference_wrapper;
- template<class T> reference_wrapper<T> ref(T & t);
- template<class T> reference_wrapper<T const> cref(T const & t);
- template<class T> class is_reference_wrapper<T const>;
- template<class T> class unwrap_reference<T const>;
-}
-
-
-template<class T> class reference_wrapper
-{
-public:
- typedef T type;
-
- explicit reference_wrapper(T & t);
-
- operator T & () const;
-
- T & get() const;
- T* get_pointer() const;
-};
-
- --- Effects: Constructs a reference_wrapper object that stores a - reference to t. -
-- Throws: Nothing. -
-
--- Returns: the stored reference. -
-- Throws: Nothing. -
-
--- Returns: the stored reference. -
-- Throws: Nothing. -
-
--- Returns: a pointer to the stored object. -
-- Throws: Nothing. -
-
-template<class T> reference_wrapper<T> ref(T & t); --
--- Returns: reference_wrapper<T>(t). -
-- Throws: Nothing. -
-
-template<class T> reference_wrapper<T const> cref(T const & t); --
--- Returns: reference_wrapper<T const>(t). -
-- Throws: Nothing. -
-
-template<class T> class is_reference_wrapper<T const>
-{
- public:
- static bool value = unspecified;
-};
-
- Value is true iff T is a specialization of reference_wrapper.
-
-template<class T> class unwrap_reference<T const>
-{
- public:
- typedef unspecified type;
-};
-
- type is equivalent to T::type if T is a
- specialization of reference_wrapper. Otherwise type is
- equivalent to T.
- - ref and cref were originally part of the Boost.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. -
-
-
-
- Copyright © 2001 by Peter Dimov and Multi Media Ltd. Permission to
- copy, use, modify, sell and distribute this document is granted provided this
- copyright notice appears in all copies. This document is provided "as
- is" without express or implied warranty, and with no claim as to its
- suitability for any purpose.