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1 /* Copyright 2003-2006 Joaquín M López Muñoz. |
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2 * Distributed under the Boost Software License, Version 1.0. |
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3 * (See 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 * See http://www.boost.org/libs/multi_index for library home page. |
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7 */ |
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8 |
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9 #ifndef BOOST_MULTI_INDEX_IDENTITY_HPP |
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10 #define BOOST_MULTI_INDEX_IDENTITY_HPP |
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11 |
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12 #if defined(_MSC_VER)&&(_MSC_VER>=1200) |
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13 #pragma once |
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14 #endif |
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15 |
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16 #include <boost/config.hpp> |
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17 #include <boost/mpl/if.hpp> |
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18 #include <boost/multi_index/identity_fwd.hpp> |
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19 #include <boost/type_traits/is_const.hpp> |
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20 #include <boost/type_traits/remove_const.hpp> |
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21 #include <boost/utility/enable_if.hpp> |
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22 |
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23 #if !defined(BOOST_NO_SFINAE) |
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24 #include <boost/type_traits/is_convertible.hpp> |
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25 #endif |
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26 |
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27 namespace boost{ |
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28 |
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29 template<class Type> class reference_wrapper; /* fwd decl. */ |
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30 |
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31 namespace multi_index{ |
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32 |
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33 namespace detail{ |
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34 |
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35 /* identity is a do-nothing key extractor that returns the [const] Type& |
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36 * object passed. |
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37 * Additionally, identity is overloaded to support referece_wrappers |
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38 * of Type and "chained pointers" to Type's. By chained pointer to Type we |
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39 * mean a type P such that, given a p of type P |
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40 * *...n...*x is convertible to Type&, for some n>=1. |
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41 * Examples of chained pointers are raw and smart pointers, iterators and |
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42 * arbitrary combinations of these (vg. Type** or auto_ptr<Type*>.) |
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43 */ |
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44 |
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45 /* NB. Some overloads of operator() have an extra dummy parameter int=0. |
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46 * This disambiguator serves several purposes: |
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47 * - Without it, MSVC++ 6.0 incorrectly regards some overloads as |
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48 * specializations of a previous member function template. |
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49 * - MSVC++ 6.0/7.0 seem to incorrectly treat some different memfuns |
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50 * as if they have the same signature. |
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51 * - If remove_const is broken due to lack of PTS, int=0 avoids the |
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52 * declaration of memfuns with identical signature. |
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53 */ |
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54 |
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55 template<typename Type> |
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56 struct const_identity_base |
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57 { |
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58 typedef Type result_type; |
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59 |
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60 template<typename ChainedPtr> |
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61 |
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62 #if !defined(BOOST_NO_SFINAE) |
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63 typename disable_if<is_convertible<const ChainedPtr&,Type&>,Type&>::type |
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64 #else |
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65 Type& |
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66 #endif |
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67 |
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68 operator()(const ChainedPtr& x)const |
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69 { |
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70 return operator()(*x); |
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71 } |
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72 |
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73 Type& operator()(Type& x)const |
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74 { |
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75 return x; |
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76 } |
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77 |
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78 Type& operator()(const reference_wrapper<Type>& x)const |
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79 { |
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80 return x.get(); |
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81 } |
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82 |
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83 Type& operator()( |
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84 const reference_wrapper<typename remove_const<Type>::type>& x,int=0)const |
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85 { |
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86 return x.get(); |
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87 } |
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88 }; |
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89 |
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90 template<typename Type> |
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91 struct non_const_identity_base |
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92 { |
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93 typedef Type result_type; |
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94 |
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95 /* templatized for pointer-like types */ |
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96 |
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97 template<typename ChainedPtr> |
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98 |
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99 #if !defined(BOOST_NO_SFINAE) |
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100 typename disable_if< |
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101 is_convertible<const ChainedPtr&,const Type&>,Type&>::type |
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102 #else |
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103 Type& |
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104 #endif |
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105 |
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106 operator()(const ChainedPtr& x)const |
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107 { |
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108 return operator()(*x); |
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109 } |
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110 |
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111 const Type& operator()(const Type& x,int=0)const |
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112 { |
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113 return x; |
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114 } |
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115 |
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116 Type& operator()(Type& x)const |
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117 { |
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118 return x; |
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119 } |
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120 |
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121 const Type& operator()(const reference_wrapper<const Type>& x,int=0)const |
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122 { |
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123 return x.get(); |
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124 } |
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125 |
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126 Type& operator()(const reference_wrapper<Type>& x)const |
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127 { |
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128 return x.get(); |
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129 } |
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130 }; |
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131 |
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132 } /* namespace multi_index::detail */ |
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133 |
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134 template<class Type> |
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135 struct identity: |
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136 mpl::if_c< |
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137 is_const<Type>::value, |
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138 detail::const_identity_base<Type>,detail::non_const_identity_base<Type> |
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139 >::type |
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140 { |
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141 }; |
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142 |
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143 } /* namespace multi_index */ |
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144 |
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145 } /* namespace boost */ |
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146 |
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147 #endif |