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include/boost/core/ref.hpp
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345
include/boost/core/ref.hpp
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#ifndef BOOST_CORE_REF_HPP
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#define BOOST_CORE_REF_HPP
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#include <boost/config.hpp>
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#include <boost/config/workaround.hpp>
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#include <boost/core/addressof.hpp>
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#include <boost/core/enable_if.hpp>
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#if defined(BOOST_HAS_PRAGMA_ONCE)
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# pragma once
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#endif
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//
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// ref.hpp - ref/cref, useful helper functions
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//
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// Copyright (C) 1999, 2000 Jaakko Jarvi (jaakko.jarvi@cs.utu.fi)
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// Copyright (C) 2001, 2002 Peter Dimov
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// Copyright (C) 2002 David Abrahams
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//
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// Copyright (C) 2014 Glen Joseph Fernandes
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// (glenjofe@gmail.com)
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//
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// Copyright (C) 2014 Agustin Berge
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//
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// Distributed under the Boost Software License, Version 1.0. (See
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// accompanying file LICENSE_1_0.txt or copy at
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// http://www.boost.org/LICENSE_1_0.txt)
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//
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// See http://www.boost.org/libs/core/doc/html/core/ref.html for documentation.
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//
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/**
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@file
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*/
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/**
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Boost namespace.
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*/
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namespace boost
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{
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#if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, == 1600 )
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struct ref_workaround_tag {};
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#endif
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namespace detail
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{
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template< class Y, class T > struct ref_convertible
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{
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typedef char (&yes) [1];
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typedef char (&no) [2];
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static yes f( T* );
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static no f( ... );
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enum _vt { value = sizeof( (f)( static_cast<Y*>(0) ) ) == sizeof(yes) };
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};
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#if defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS)
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struct ref_empty
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{
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};
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#endif
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} // namespace detail
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// reference_wrapper
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/**
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@brief Contains a reference to an object of type `T`.
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`reference_wrapper` is primarily used to "feed" references to
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function templates (algorithms) that take their parameter by
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value. It provides an implicit conversion to `T&`, which
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usually allows the function templates to work on references
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unmodified.
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*/
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template<class T> class reference_wrapper
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{
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public:
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/**
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Type `T`.
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*/
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typedef T type;
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/**
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Constructs a `reference_wrapper` object that stores a
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reference to `t`.
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@remark Does not throw.
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*/
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BOOST_FORCEINLINE explicit reference_wrapper(T& t) BOOST_NOEXCEPT : t_(boost::addressof(t)) {}
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#if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, == 1600 )
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BOOST_FORCEINLINE explicit reference_wrapper( T & t, ref_workaround_tag ) BOOST_NOEXCEPT : t_( boost::addressof( t ) ) {}
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#endif
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#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
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/**
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@remark Construction from a temporary object is disabled.
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*/
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BOOST_DELETED_FUNCTION(reference_wrapper(T&& t))
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public:
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#endif
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template<class Y> friend class reference_wrapper;
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/**
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Constructs a `reference_wrapper` object that stores the
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reference stored in the compatible `reference_wrapper` `r`.
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@remark Only enabled when `Y*` is convertible to `T*`.
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@remark Does not throw.
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*/
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#if !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS)
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template<class Y, class = typename enable_if_c<boost::detail::ref_convertible<Y, T>::value>::type>
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reference_wrapper( reference_wrapper<Y> r ) BOOST_NOEXCEPT : t_( r.t_ )
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{
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}
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#else
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template<class Y> reference_wrapper( reference_wrapper<Y> r,
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typename enable_if_c<boost::detail::ref_convertible<Y, T>::value,
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boost::detail::ref_empty>::type = boost::detail::ref_empty() ) BOOST_NOEXCEPT : t_( r.t_ )
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{
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}
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#endif
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/**
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@return The stored reference.
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@remark Does not throw.
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*/
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BOOST_FORCEINLINE operator T& () const BOOST_NOEXCEPT { return *t_; }
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/**
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@return The stored reference.
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@remark Does not throw.
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*/
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BOOST_FORCEINLINE T& get() const BOOST_NOEXCEPT { return *t_; }
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/**
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@return A pointer to the object referenced by the stored
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reference.
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@remark Does not throw.
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*/
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BOOST_FORCEINLINE T* get_pointer() const BOOST_NOEXCEPT { return t_; }
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private:
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T* t_;
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};
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// ref
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/**
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@cond
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*/
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#if defined( BOOST_BORLANDC ) && BOOST_WORKAROUND( BOOST_BORLANDC, BOOST_TESTED_AT(0x581) )
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# define BOOST_REF_CONST
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#else
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# define BOOST_REF_CONST const
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#endif
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/**
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@endcond
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*/
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/**
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@return `reference_wrapper<T>(t)`
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@remark Does not throw.
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*/
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template<class T> BOOST_FORCEINLINE reference_wrapper<T> BOOST_REF_CONST ref( T & t ) BOOST_NOEXCEPT
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{
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#if defined( BOOST_MSVC ) && BOOST_WORKAROUND( BOOST_MSVC, == 1600 )
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return reference_wrapper<T>( t, ref_workaround_tag() );
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#else
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return reference_wrapper<T>( t );
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#endif
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}
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// cref
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/**
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@return `reference_wrapper<T const>(t)`
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@remark Does not throw.
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*/
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template<class T> BOOST_FORCEINLINE reference_wrapper<T const> BOOST_REF_CONST cref( T const & t ) BOOST_NOEXCEPT
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{
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return reference_wrapper<T const>(t);
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}
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#undef BOOST_REF_CONST
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#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
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/**
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@cond
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*/
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#if defined(BOOST_NO_CXX11_DELETED_FUNCTIONS)
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# define BOOST_REF_DELETE
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#else
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# define BOOST_REF_DELETE = delete
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#endif
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/**
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@endcond
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*/
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/**
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@remark Construction from a temporary object is disabled.
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*/
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template<class T> void ref(T const&&) BOOST_REF_DELETE;
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/**
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@remark Construction from a temporary object is disabled.
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*/
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template<class T> void cref(T const&&) BOOST_REF_DELETE;
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#undef BOOST_REF_DELETE
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#endif
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// is_reference_wrapper
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/**
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@brief Determine if a type `T` is an instantiation of
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`reference_wrapper`.
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The value static constant will be true if the type `T` is a
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specialization of `reference_wrapper`.
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*/
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template<typename T> struct is_reference_wrapper
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{
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BOOST_STATIC_CONSTANT( bool, value = false );
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};
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/**
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@cond
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*/
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template<typename T> struct is_reference_wrapper< reference_wrapper<T> >
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{
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BOOST_STATIC_CONSTANT( bool, value = true );
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};
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#if !defined(BOOST_NO_CV_SPECIALIZATIONS)
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template<typename T> struct is_reference_wrapper< reference_wrapper<T> const >
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{
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BOOST_STATIC_CONSTANT( bool, value = true );
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};
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template<typename T> struct is_reference_wrapper< reference_wrapper<T> volatile >
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{
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BOOST_STATIC_CONSTANT( bool, value = true );
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};
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template<typename T> struct is_reference_wrapper< reference_wrapper<T> const volatile >
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{
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BOOST_STATIC_CONSTANT( bool, value = true );
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};
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#endif // !defined(BOOST_NO_CV_SPECIALIZATIONS)
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/**
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@endcond
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*/
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// unwrap_reference
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/**
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@brief Find the type in a `reference_wrapper`.
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The `typedef` type is `T::type` if `T` is a
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`reference_wrapper`, `T` otherwise.
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*/
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template<typename T> struct unwrap_reference
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{
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typedef T type;
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};
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/**
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@cond
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*/
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template<typename T> struct unwrap_reference< reference_wrapper<T> >
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{
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typedef T type;
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};
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#if !defined(BOOST_NO_CV_SPECIALIZATIONS)
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template<typename T> struct unwrap_reference< reference_wrapper<T> const >
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{
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typedef T type;
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};
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template<typename T> struct unwrap_reference< reference_wrapper<T> volatile >
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{
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typedef T type;
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};
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template<typename T> struct unwrap_reference< reference_wrapper<T> const volatile >
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{
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typedef T type;
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};
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#endif // !defined(BOOST_NO_CV_SPECIALIZATIONS)
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/**
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@endcond
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*/
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// unwrap_ref
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/**
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@return `unwrap_reference<T>::type&(t)`
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@remark Does not throw.
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*/
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template<class T> BOOST_FORCEINLINE typename unwrap_reference<T>::type& unwrap_ref( T & t ) BOOST_NOEXCEPT
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{
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return t;
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}
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// get_pointer
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/**
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@cond
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*/
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template<class T> BOOST_FORCEINLINE T* get_pointer( reference_wrapper<T> const & r ) BOOST_NOEXCEPT
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{
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return r.get_pointer();
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}
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/**
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@endcond
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*/
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} // namespace boost
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#endif // #ifndef BOOST_CORE_REF_HPP
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