boost/serialization/state_saver.hpp

   1 #ifndef BOOST_SERIALIZATION_STATE_SAVER_HPP
   2 #define BOOST_SERIALIZATION_STATE_SAVER_HPP
   3
   4 // MS compatible compilers support #pragma once
   5 #if defined(_MSC_VER) && (_MSC_VER >= 1020)
   6 # pragma once
   7 #endif
   8
   9 /////////1/////////2/////////3/////////4/////////5/////////6/////////7/////////8
  10 // state_saver.hpp:
  11
  12 // (C) Copyright 2003-4 Pavel Vozenilek and Robert Ramey - http://www.rrsd.com.
  13 // Use, modification and distribution is subject to the Boost Software
  14 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
  15 // http://www.boost.org/LICENSE_1_0.txt)
  16
  17 //  See http://www.boost.org/libs/serialization for updates, documentation, and revision history.
  18
  19 // Inspired by Daryle Walker's iostate_saver concept.  This saves the original
  20 // value of a variable when a state_saver is constructed and restores
  21 // upon destruction.  Useful for being sure that state is restored to
  22 // variables upon exit from scope.
  23
  24
  25 #include <boost/config.hpp>
  26 #ifndef BOOST_NO_EXCEPTIONS
  27     #include <exception>
  28 #endif
  29
  30 #include <boost/call_traits.hpp>
  31 #include <boost/noncopyable.hpp>
  32 #include <boost/type_traits/has_nothrow_copy.hpp>
  33 #include <boost/detail/no_exceptions_support.hpp>
  34
  35 #include <boost/mpl/eval_if.hpp>
  36 #include <boost/mpl/identity.hpp>
  37
  38 namespace boost {
  39 namespace serialization {
  40
  41 template<class T>
  42 // T requirements:
  43 //  - POD or object semantic (cannot be reference, function, ...)
  44 //  - copy constructor
  45 //  - operator = (no-throw one preferred)
  46 class state_saver : private boost::noncopyable
  47 {
  48 private:
  49     const T previous_value;
  50     T & previous_ref;
  51
  52     struct restore {
  53         static void invoke(T & previous_ref, const T & previous_value){
  54             previous_ref = previous_value; // won't throw
  55         }
  56     };
  57
  58     struct restore_with_exception {
  59         static void invoke(T & previous_ref, const T & previous_value){
  60             BOOST_TRY{
  61                 previous_ref = previous_value;
  62             }
  63             BOOST_CATCH(::std::exception &) {
  64                 // we must ignore it - we are in destructor
  65             }
  66             BOOST_CATCH_END
  67         }
  68     };
  69
  70 public:
  71     state_saver(
  72         T & object
  73     ) :
  74         previous_value(object),
  75         previous_ref(object)
  76     {}
  77
  78     ~state_saver() {
  79         #ifndef BOOST_NO_EXCEPTIONS
  80             typedef BOOST_DEDUCED_TYPENAME mpl::eval_if<
  81                 has_nothrow_copy<T>,
  82                 mpl::identity<restore>,
  83                 mpl::identity<restore_with_exception>
  84             >::type typex;
  85             typex::invoke(previous_ref, previous_value);
  86         #else
  87             previous_ref = previous_value;
  88         #endif
  89     }
  90
  91 }; // state_saver<>
  92
  93 } // serialization
  94 } // boost
  95
  96 #endif //BOOST_SERIALIZATION_STATE_SAVER_HPP