[857] | 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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