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#ifndef BOOST_STATE_SAVER_HPP
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#define BOOST_STATE_SAVER_HPP
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// MS compatible compilers support #pragma once
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#if defined(_MSC_VER) && (_MSC_VER >= 1020)
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# pragma once
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#endif
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/////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
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// state_saver.hpp:
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// (C) Copyright 2003-4 Pavel Vozenilek and Robert Ramey - http://www.rrsd.com.
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// Use, modification and distribution is subject to the Boost Software
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// License, Version 1.0. (See 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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// See http://www.boost.org for updates, documentation, and revision history.
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// Inspired by Daryle Walker's iostate_saver concept. This saves the original
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// value of a variable when a state_saver is constructed and restores
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// upon destruction. Useful for being sure that state is restored to
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// variables upon exit from scope.
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#include <boost/config.hpp>
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#ifndef BOOST_NO_EXCEPTIONS
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#include <exception>
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#endif
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#include <boost/call_traits.hpp>
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#include <boost/noncopyable.hpp>
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#include <boost/type_traits/has_nothrow_copy.hpp>
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#include <boost/detail/no_exceptions_support.hpp>
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#include <boost/mpl/eval_if.hpp>
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#include <boost/mpl/identity.hpp>
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namespace boost {
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template<class T>
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// T requirements:
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// - POD or object semantic (cannot be reference, function, ...)
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// - copy constructor
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// - operator = (no-throw one preferred)
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class state_saver : private boost::noncopyable
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{
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private:
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const T previous_value;
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T & previous_ref;
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struct restore {
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static void invoke(T & previous_ref, const T & previous_value){
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previous_ref = previous_value; // won't throw
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}
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};
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struct restore_with_exception {
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static void invoke(T & previous_ref, const T & previous_value){
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BOOST_TRY{
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previous_ref = previous_value;
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}
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BOOST_CATCH(::std::exception &) {
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// we must ignore it - we are in destructor
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}
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BOOST_CATCH_END
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}
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};
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public:
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state_saver(
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T & object
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) :
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previous_value(object),
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previous_ref(object)
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{}
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~state_saver() {
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#ifndef BOOST_NO_EXCEPTIONS
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typedef BOOST_DEDUCED_TYPENAME mpl::eval_if<
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has_nothrow_copy<T>,
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mpl::identity<restore>,
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mpl::identity<restore_with_exception>
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>::type typex;
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typex::invoke(previous_ref, previous_value);
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#else
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previous_ref = previous_value;
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#endif
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}
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}; // state_saver<>
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} // boost
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#endif //BOOST_STATE_SAVER_HPP
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