1 | // Copyright Daniel Wallin, David Abrahams 2005. Use, modification and
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2 | // distribution is subject to the Boost Software License, Version 1.0. (See
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3 | // accompanying file LICENSE_1_0.txt or copy at
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4 | // http://www.boost.org/LICENSE_1_0.txt)
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5 |
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6 | #ifndef ARG_LIST_050329_HPP
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7 | #define ARG_LIST_050329_HPP
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8 |
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9 | #include <boost/parameter/aux_/void.hpp>
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10 | #include <boost/parameter/aux_/result_of0.hpp>
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11 | #include <boost/parameter/aux_/default.hpp>
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12 | #include <boost/parameter/aux_/parameter_requirements.hpp>
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13 | #include <boost/parameter/config.hpp>
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14 |
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15 | #include <boost/mpl/apply.hpp>
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16 |
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17 | #include <boost/type_traits/add_reference.hpp>
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18 | #include <boost/type_traits/is_same.hpp>
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19 |
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20 | #include <boost/preprocessor/repetition/enum_params.hpp>
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21 | #include <boost/preprocessor/facilities/intercept.hpp>
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22 |
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23 | namespace boost { namespace parameter {
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24 |
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25 | // Forward declaration for aux::arg_list, below.
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26 | template<class T> struct keyword;
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27 |
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28 | namespace aux {
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29 |
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30 | //
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31 | // Structures used to build the tuple of actual arguments. The
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32 | // tuple is a nested cons-style list of arg_list specializations
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33 | // terminated by an empty_arg_list.
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34 | //
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35 | // Each specialization of arg_list is derived from its successor in
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36 | // the list type. This feature is used along with using
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37 | // declarations to build member function overload sets that can
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38 | // match against keywords.
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39 | //
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40 |
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41 | // Terminates arg_list<> and represents an empty list. Since this
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42 | // is just the terminating case you might want to look at arg_list
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43 | // first, to get a feel for what's really happening here.
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44 | struct empty_arg_list
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45 | {
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46 | empty_arg_list() {}
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47 |
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48 | // Constructor taking BOOST_PARAMETER_MAX_ARITY empty_arg_list
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49 | // arguments; this makes initialization
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50 | empty_arg_list(
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51 | BOOST_PP_ENUM_PARAMS(
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52 | BOOST_PARAMETER_MAX_ARITY, void_ BOOST_PP_INTERCEPT
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53 | ))
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54 | {}
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55 |
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56 | // A metafunction class that, given a keyword and a default
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57 | // type, returns the appropriate result type for a keyword
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58 | // lookup given that default
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59 | struct binding
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60 | {
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61 | template<class KW, class Default>
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62 | struct apply
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63 | {
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64 | typedef Default type;
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65 | };
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66 | };
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67 |
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68 | #if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) \
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69 | || (BOOST_WORKAROUND(__GNUC__, < 3)) \
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70 | || BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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71 |
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72 | // The overload set technique doesn't work with these older
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73 | // compilers, so they need some explicit handholding.
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74 |
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75 | // A metafunction class that, given a keyword, returns the type
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76 | // of the base sublist whose get() function can produce the
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77 | // value for that key
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78 | struct key_owner
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79 | {
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80 | template<class KW>
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81 | struct apply
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82 | {
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83 | typedef empty_arg_list type;
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84 | };
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85 | };
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86 |
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87 | template <class K, class T>
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88 | T& get(default_<K,T> x) const
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89 | {
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90 | return x.value;
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91 | }
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92 |
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93 | template <class K, class F>
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94 | typename result_of0<F>::type
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95 | get(lazy_default<K,F> x) const
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96 | {
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97 | return x.compute_default();
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98 | }
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99 | #endif
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100 |
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101 | // If this function is called, it means there is no argument
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102 | // in the list that matches the supplied keyword. Just return
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103 | // the default value.
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104 | template <class K, class Default>
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105 | Default& operator[](default_<K, Default> x) const
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106 | {
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107 | return x.value;
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108 | }
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109 |
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110 | // If this function is called, it means there is no argument
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111 | // in the list that matches the supplied keyword. Just evaluate
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112 | // and return the default value.
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113 | template <class K, class F>
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114 | typename result_of0<F>::type
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115 | operator[](
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116 | BOOST_PARAMETER_lazy_default_fallback<K,F> x) const
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117 | {
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118 | return x.compute_default();
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119 | }
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120 |
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121 | // No argument corresponding to ParameterRequirements::key_type
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122 | // was found if we match this overload, so unless that parameter
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123 | // has a default, we indicate that the actual arguments don't
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124 | // match the function's requirements.
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125 | template <class ParameterRequirements>
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126 | static typename ParameterRequirements::has_default
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127 | satisfies(ParameterRequirements*);
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128 | };
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129 |
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130 | // Forward declaration for arg_list::operator,
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131 | template <class KW, class T>
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132 | struct tagged_argument;
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133 |
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134 | // A tuple of tagged arguments, terminated with empty_arg_list.
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135 | // Every TaggedArg is an instance of tagged_argument<>.
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136 | template <class TaggedArg, class Next = empty_arg_list>
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137 | struct arg_list : Next
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138 | {
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139 | typedef arg_list<TaggedArg,Next> self;
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140 | typedef typename TaggedArg::key_type key_type;
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141 | typedef typename TaggedArg::value_type value_type;
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142 | typedef typename TaggedArg::reference reference;
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143 |
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144 | TaggedArg arg; // Stores the argument
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145 |
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146 | // Store the arguments in successive nodes of this list
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147 | template< // class A0, class A1, ...
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148 | BOOST_PP_ENUM_PARAMS(BOOST_PARAMETER_MAX_ARITY, class A)
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149 | >
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150 | arg_list( // A0 const& a0, A1 const& a1, ...
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151 | BOOST_PP_ENUM_BINARY_PARAMS(BOOST_PARAMETER_MAX_ARITY, A, const & a)
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152 | )
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153 | : Next( // a1, a2, ...
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154 | BOOST_PP_ENUM_SHIFTED_PARAMS(BOOST_PARAMETER_MAX_ARITY, a)
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155 | , void_()
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156 | )
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157 | , arg(a0)
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158 | {}
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159 |
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160 | // Create a new list by prepending arg to a copy of tail. Used
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161 | // when incrementally building this structure with the comma
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162 | // operator.
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163 | arg_list(TaggedArg arg, Next const& tail)
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164 | : Next(tail)
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165 | , arg(arg)
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166 | {}
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167 |
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168 |
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169 | // A metafunction class that, given a keyword and a default
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170 | // type, returns the appropriate result type for a keyword
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171 | // lookup given that default
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172 | struct binding
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173 | {
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174 | template <class KW, class Default>
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175 | struct apply
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176 | {
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177 | typedef typename mpl::eval_if<
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178 | boost::is_same<KW, key_type>
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179 | , mpl::identity<reference>
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180 | , mpl::apply_wrap2<typename Next::binding, KW, Default>
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181 | >::type type;
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182 | };
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183 | };
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184 |
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185 | //
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186 | // Begin implementation of indexing operators for looking up
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187 | // specific arguments by name
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188 | //
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189 |
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190 | #if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) \
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191 | || BOOST_WORKAROUND(__GNUC__, < 3) \
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192 | || BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
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193 | // These older compilers don't support the overload set creation
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194 | // idiom well, so we need to do all the return type calculation
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195 | // for the compiler and dispatch through an outer function template
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196 |
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197 | // A metafunction class that, given a keyword, returns the base
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198 | // sublist whose get() function can produce the value for that
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199 | // key.
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200 | struct key_owner
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201 | {
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202 | template<class KW>
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203 | struct apply
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204 | {
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205 | typedef typename mpl::eval_if<
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206 | boost::is_same<KW, key_type>
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207 | , mpl::identity<arg_list<TaggedArg,Next> >
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208 | , mpl::apply_wrap1<typename Next::key_owner,KW>
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209 | >::type type;
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210 | };
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211 | };
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212 |
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213 | // Outer indexing operators that dispatch to the right node's
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214 | // get() function.
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215 | template <class KW>
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216 | typename mpl::apply_wrap2<binding, KW, void_>::type
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217 | operator[](keyword<KW> const& x) const
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218 | {
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219 | typename mpl::apply_wrap1<key_owner, KW>::type const& sublist = *this;
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220 | return sublist.get(x);
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221 | }
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222 |
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223 | template <class KW, class Default>
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224 | typename mpl::apply_wrap2<binding, KW, Default&>::type
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225 | operator[](default_<KW, Default> x) const
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226 | {
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227 | typename mpl::apply_wrap1<key_owner, KW>::type const& sublist = *this;
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228 | return sublist.get(x);
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229 | }
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230 |
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231 | template <class KW, class F>
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232 | typename mpl::apply_wrap2<
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233 | binding,KW
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234 | , typename result_of0<F>::type
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235 | >::type
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236 | operator[](lazy_default<KW,F> x) const
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237 | {
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238 | typename mpl::apply_wrap1<key_owner, KW>::type const& sublist = *this;
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239 | return sublist.get(x);
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240 | }
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241 |
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242 | // These just return the stored value; when empty_arg_list is
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243 | // reached, indicating no matching argument was passed, the
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244 | // default is returned, or if no default_ or lazy_default was
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245 | // passed, compilation fails.
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246 | reference get(keyword<key_type> const&) const
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247 | {
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248 | return arg.value;
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249 | }
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250 |
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251 | template <class Default>
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252 | reference get(default_<key_type,Default>) const
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253 | {
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254 | return arg.value;
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255 | }
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256 |
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257 | template <class Default>
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258 | reference get(lazy_default<key_type, Default>) const
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259 | {
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260 | return arg.value;
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261 | }
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262 |
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263 | #else
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264 |
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265 | reference operator[](keyword<key_type> const&) const
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266 | {
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267 | return arg.value;
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268 | }
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269 |
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270 | template <class Default>
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271 | reference operator[](default_<key_type, Default>) const
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272 | {
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273 | return arg.value;
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274 | }
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275 |
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276 | template <class Default>
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277 | reference operator[](lazy_default<key_type, Default>) const
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278 | {
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279 | return arg.value;
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280 | }
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281 |
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282 | // Builds an overload set including operator[]s defined in base
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283 | // classes.
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284 | using Next::operator[];
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285 |
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286 | //
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287 | // End of indexing support
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288 | //
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289 |
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290 |
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291 | //
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292 | // For parameter_requirements matching this node's key_type,
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293 | // return a bool constant wrapper indicating whether the
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294 | // requirements are satisfied by TaggedArg. Used only for
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295 | // compile-time computation and never really called, so a
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296 | // declaration is enough.
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297 | //
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298 | template <class HasDefault, class Predicate>
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299 | static typename mpl::apply1<Predicate, value_type>::type
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300 | satisfies(
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301 | parameter_requirements<key_type,Predicate,HasDefault>*
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302 | );
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303 |
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304 | // Builds an overload set including satisfies functions defined
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305 | // in base classes.
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306 | using Next::satisfies;
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307 | #endif
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308 |
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309 | // Comma operator to compose argument list without using parameters<>.
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310 | // Useful for argument lists with undetermined length.
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311 | template <class KW, class T2>
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312 | arg_list<tagged_argument<KW, T2>, self>
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313 | operator,(tagged_argument<KW,T2> x)
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314 | {
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315 | return arg_list<tagged_argument<KW,T2>, self>(x, *this);
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316 | }
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317 | };
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318 |
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319 | #if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) // ETI workaround
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320 | template <> struct arg_list<int,int> {};
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321 | #endif
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322 |
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323 | }}} // namespace boost::parameter::aux
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324 |
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325 | #endif // ARG_LIST_050329_HPP
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326 |
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