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1 // Copyright Daniel Wallin 2006. Use, modification and distribution is |
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2 // subject to the Boost Software License, Version 1.0. (See accompanying |
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3 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt) |
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4 |
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5 #ifndef BOOST_PARAMETER_VALUE_TYPE_060921_HPP |
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6 # define BOOST_PARAMETER_VALUE_TYPE_060921_HPP |
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7 |
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8 # include <boost/mpl/apply.hpp> |
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9 # include <boost/mpl/assert.hpp> |
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10 # include <boost/mpl/and.hpp> |
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11 # include <boost/parameter/aux_/result_of0.hpp> |
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12 # include <boost/parameter/aux_/void.hpp> |
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13 # include <boost/type_traits/is_same.hpp> |
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14 |
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15 # if BOOST_WORKAROUND(BOOST_MSVC, < 1300) |
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16 # include <boost/mpl/eval_if.hpp> |
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17 # endif |
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18 |
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19 namespace boost { namespace parameter { |
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20 |
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21 // A metafunction that, given an argument pack, returns the type of |
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22 // the parameter identified by the given keyword. If no such |
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23 // parameter has been specified, returns Default |
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24 |
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25 # if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) \ |
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26 || BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564)) |
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27 template <class Parameters, class Keyword, class Default> |
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28 struct value_type0 |
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29 { |
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30 typedef typename mpl::apply_wrap3< |
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31 typename Parameters::binding,Keyword,Default,mpl::false_ |
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32 >::type type; |
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33 |
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34 BOOST_MPL_ASSERT_NOT(( |
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35 mpl::and_< |
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36 is_same<Default, void_> |
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37 , is_same<type, void_> |
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38 > |
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39 )); |
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40 }; |
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41 # endif |
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42 |
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43 template <class Parameters, class Keyword, class Default = void_> |
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44 # if !BOOST_WORKAROUND(BOOST_MSVC, < 1300) |
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45 struct value_type |
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46 # else |
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47 struct value_type_eti |
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48 # endif |
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49 { |
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50 # if BOOST_WORKAROUND(BOOST_MSVC, <= 1300) \ |
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51 || BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564)) |
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52 typedef typename mpl::eval_if< |
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53 mpl::is_placeholder<Parameters> |
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54 , mpl::identity<int> |
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55 , value_type0<Parameters,Keyword,Default> |
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56 >::type type; |
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57 # else |
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58 typedef typename mpl::apply_wrap3< |
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59 typename Parameters::binding,Keyword,Default,mpl::false_ |
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60 >::type type; |
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61 |
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62 BOOST_MPL_ASSERT_NOT(( |
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63 mpl::and_< |
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64 is_same<Default, void_> |
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65 , is_same<type, void_> |
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66 > |
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67 )); |
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68 # endif |
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69 |
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70 # if !BOOST_WORKAROUND(BOOST_MSVC, < 1300) |
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71 BOOST_MPL_AUX_LAMBDA_SUPPORT(3,value_type,(Parameters,Keyword,Default)) |
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72 # endif |
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73 }; |
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74 |
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75 # if BOOST_WORKAROUND(BOOST_MSVC, < 1300) |
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76 template <class Parameters, class Keyword, class Default = void_> |
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77 struct value_type |
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78 { |
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79 typedef typename mpl::eval_if< |
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80 is_same<Parameters, int> |
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81 , mpl::identity<int> |
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82 , value_type_eti<Parameters, Keyword, Default> |
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83 >::type type; |
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84 |
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85 BOOST_MPL_AUX_LAMBDA_SUPPORT(3,value_type,(Parameters,Keyword,Default)) |
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86 }; |
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87 # endif |
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88 |
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89 // A metafunction that, given an argument pack, returns the type of |
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90 // the parameter identified by the given keyword. If no such |
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91 // parameter has been specified, returns the type returned by invoking |
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92 // DefaultFn |
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93 template <class Parameters, class Keyword, class DefaultFn> |
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94 struct lazy_value_type |
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95 { |
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96 typedef typename mpl::apply_wrap3< |
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97 typename Parameters::binding |
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98 , Keyword |
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99 , typename aux::result_of0<DefaultFn>::type |
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100 , mpl::false_ |
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101 >::type type; |
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102 }; |
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103 |
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104 |
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105 }} // namespace boost::parameter |
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106 |
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107 #endif // BOOST_PARAMETER_VALUE_TYPE_060921_HPP |
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108 |