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1 //-----------------------------------------------------------------------------
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2 // boost variant/visitor_ptr.hpp header file
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3 // See http://www.boost.org for updates, documentation, and revision history.
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4 //-----------------------------------------------------------------------------
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5 //
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6 // Copyright (c) 2002-2003
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7 // Eric Friedman
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8 //
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9 // Distributed under the Boost Software License, Version 1.0. (See
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10 // accompanying file LICENSE_1_0.txt or copy at
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11 // http://www.boost.org/LICENSE_1_0.txt)
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12
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13 #ifndef BOOST_VARIANT_VISITOR_PTR_HPP
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14 #define BOOST_VARIANT_VISITOR_PTR_HPP
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15
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16 #include "boost/variant/bad_visit.hpp"
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17 #include "boost/variant/static_visitor.hpp"
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18
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19 #include "boost/mpl/eval_if.hpp"
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20 #include "boost/mpl/identity.hpp"
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21 #include "boost/throw_exception.hpp"
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22 #include "boost/type_traits/add_reference.hpp"
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23 #include "boost/type_traits/is_reference.hpp"
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24 #include "boost/type_traits/is_void.hpp"
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25
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26 namespace boost {
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27
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28 //////////////////////////////////////////////////////////////////////////
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29 // function template visitor_ptr
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30 //
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31 // Adapts a function pointer for use as visitor capable of handling
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32 // values of a single type. Throws bad_visit if inappropriately applied.
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33 //
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34 template <typename T, typename R>
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35 class visitor_ptr_t
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36 : public static_visitor<R>
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37 {
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38 private: // representation
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39
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40 typedef R (*visitor_t)(T);
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41
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42 visitor_t visitor_;
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43
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44 public: // typedefs
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45
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46 typedef R result_type;
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47
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48 private: // private typedefs
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49
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50 typedef typename mpl::eval_if<
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51 is_reference<T>
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52 , mpl::identity<T>
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53 , add_reference<const T>
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54 >::type argument_fwd_type;
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55
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56 public: // structors
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57
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58 explicit visitor_ptr_t(visitor_t visitor) BOOST_NOEXCEPT
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59 : visitor_(visitor)
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60 {
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61 }
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62
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63 public: // static visitor interfaces
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64
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65 template <typename U>
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66 result_type operator()(const U&) const
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67 {
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68 boost::throw_exception(bad_visit());
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69 }
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70
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71 #if !defined(BOOST_NO_VOID_RETURNS)
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72
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73 public: // static visitor interfaces, cont.
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74
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75 result_type operator()(argument_fwd_type operand) const
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76 {
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77 return visitor_(operand);
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78 }
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79
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80 #else // defined(BOOST_NO_VOID_RETURNS)
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81
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82 private: // helpers, for static visitor interfaces (below)
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83
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84 result_type execute_impl(argument_fwd_type operand, mpl::false_) const
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85 {
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86 return visitor_(operand);
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87 }
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88
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89 BOOST_VARIANT_AUX_RETURN_VOID_TYPE
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90 execute_impl(argument_fwd_type operand, mpl::true_) const
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91 {
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92 visitor_(operand);
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93 BOOST_VARIANT_AUX_RETURN_VOID;
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94 }
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95
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96 public: // static visitor interfaces, cont.
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97
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98 BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(result_type)
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99 operator()(argument_fwd_type operand) const
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100 {
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101 typedef typename is_void<result_type>::type has_void_result;
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102 return execute_impl(operand, has_void_result());
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103 }
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104
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105 #endif // BOOST_NO_VOID_RETURNS workaround
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106
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107 };
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108
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109 template <typename R, typename T>
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110 inline visitor_ptr_t<T,R> visitor_ptr(R (*visitor)(T))
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111 {
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112 return visitor_ptr_t<T,R>(visitor);
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113 }
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114
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115 } // namespace boost
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116
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117 #endif// BOOST_VISITOR_VISITOR_PTR_HPP
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