1 | // Boost Lambda Library -- if.hpp ------------------------------------------ |
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2 | |
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3 | // Copyright (C) 1999, 2000 Jaakko Järvi (jaakko.jarvi@cs.utu.fi) |
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4 | // Copyright (C) 2000 Gary Powell (powellg@amazon.com) |
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5 | // Copyright (C) 2001-2002 Joel de Guzman |
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6 | // |
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7 | // Distributed under the Boost Software License, Version 1.0. (See |
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8 | // accompanying file LICENSE_1_0.txt or copy at |
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9 | // http://www.boost.org/LICENSE_1_0.txt) |
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10 | // |
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11 | // For more information, see www.boost.org |
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12 | |
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13 | // -------------------------------------------------------------------------- |
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14 | |
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15 | #if !defined(BOOST_LAMBDA_IF_HPP) |
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16 | #define BOOST_LAMBDA_IF_HPP |
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17 | |
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18 | #include "boost/lambda/core.hpp" |
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19 | |
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20 | // Arithmetic type promotion needed for if_then_else_return |
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21 | #include "boost/lambda/detail/operator_actions.hpp" |
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22 | #include "boost/lambda/detail/operator_return_type_traits.hpp" |
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23 | |
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24 | namespace boost { |
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25 | namespace lambda { |
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26 | |
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27 | // -- if control construct actions ---------------------- |
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28 | |
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29 | class ifthen_action {}; |
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30 | class ifthenelse_action {}; |
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31 | class ifthenelsereturn_action {}; |
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32 | |
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33 | // Specialization for if_then. |
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34 | template<class Args> |
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35 | class |
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36 | lambda_functor_base<ifthen_action, Args> { |
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37 | public: |
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38 | Args args; |
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39 | template <class T> struct sig { typedef void type; }; |
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40 | public: |
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41 | explicit lambda_functor_base(const Args& a) : args(a) {} |
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42 | |
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43 | template<class RET, CALL_TEMPLATE_ARGS> |
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44 | RET call(CALL_FORMAL_ARGS) const { |
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45 | if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) |
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46 | detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); |
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47 | } |
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48 | }; |
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49 | |
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50 | // If Then |
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51 | template <class Arg1, class Arg2> |
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52 | inline const |
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53 | lambda_functor< |
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54 | lambda_functor_base< |
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55 | ifthen_action, |
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56 | tuple<lambda_functor<Arg1>, lambda_functor<Arg2> > |
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57 | > |
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58 | > |
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59 | if_then(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2) { |
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60 | return |
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61 | lambda_functor_base< |
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62 | ifthen_action, |
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63 | tuple<lambda_functor<Arg1>, lambda_functor<Arg2> > |
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64 | > |
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65 | ( tuple<lambda_functor<Arg1>, lambda_functor<Arg2> >(a1, a2) ); |
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66 | } |
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67 | |
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68 | |
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69 | // Specialization for if_then_else. |
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70 | template<class Args> |
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71 | class |
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72 | lambda_functor_base<ifthenelse_action, Args> { |
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73 | public: |
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74 | Args args; |
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75 | template <class T> struct sig { typedef void type; }; |
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76 | public: |
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77 | explicit lambda_functor_base(const Args& a) : args(a) {} |
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78 | |
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79 | template<class RET, CALL_TEMPLATE_ARGS> |
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80 | RET call(CALL_FORMAL_ARGS) const { |
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81 | if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) |
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82 | detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS); |
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83 | else |
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84 | detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS); |
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85 | } |
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86 | }; |
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87 | |
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88 | |
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89 | |
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90 | // If then else |
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91 | |
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92 | template <class Arg1, class Arg2, class Arg3> |
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93 | inline const |
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94 | lambda_functor< |
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95 | lambda_functor_base< |
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96 | ifthenelse_action, |
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97 | tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> > |
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98 | > |
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99 | > |
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100 | if_then_else(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2, |
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101 | const lambda_functor<Arg3>& a3) { |
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102 | return |
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103 | lambda_functor_base< |
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104 | ifthenelse_action, |
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105 | tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> > |
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106 | > |
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107 | (tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> > |
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108 | (a1, a2, a3) ); |
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109 | } |
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110 | |
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111 | // Our version of operator?:() |
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112 | |
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113 | template <class Arg1, class Arg2, class Arg3> |
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114 | inline const |
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115 | lambda_functor< |
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116 | lambda_functor_base< |
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117 | other_action<ifthenelsereturn_action>, |
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118 | tuple<lambda_functor<Arg1>, |
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119 | typename const_copy_argument<Arg2>::type, |
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120 | typename const_copy_argument<Arg3>::type> |
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121 | > |
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122 | > |
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123 | if_then_else_return(const lambda_functor<Arg1>& a1, |
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124 | const Arg2 & a2, |
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125 | const Arg3 & a3) { |
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126 | return |
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127 | lambda_functor_base< |
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128 | other_action<ifthenelsereturn_action>, |
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129 | tuple<lambda_functor<Arg1>, |
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130 | typename const_copy_argument<Arg2>::type, |
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131 | typename const_copy_argument<Arg3>::type> |
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132 | > ( tuple<lambda_functor<Arg1>, |
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133 | typename const_copy_argument<Arg2>::type, |
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134 | typename const_copy_argument<Arg3>::type> (a1, a2, a3) ); |
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135 | } |
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136 | |
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137 | namespace detail { |
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138 | |
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139 | // return type specialization for conditional expression begins ----------- |
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140 | // start reading below and move upwards |
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141 | |
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142 | // PHASE 6:1 |
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143 | // check if A is conbertible to B and B to A |
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144 | template<int Phase, bool AtoB, bool BtoA, bool SameType, class A, class B> |
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145 | struct return_type_2_ifthenelsereturn; |
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146 | |
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147 | // if A can be converted to B and vice versa -> ambiguous |
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148 | template<int Phase, class A, class B> |
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149 | struct return_type_2_ifthenelsereturn<Phase, true, true, false, A, B> { |
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150 | typedef |
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151 | detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type; |
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152 | // ambiguous type in conditional expression |
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153 | }; |
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154 | // if A can be converted to B and vice versa and are of same type |
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155 | template<int Phase, class A, class B> |
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156 | struct return_type_2_ifthenelsereturn<Phase, true, true, true, A, B> { |
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157 | typedef A type; |
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158 | }; |
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159 | |
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160 | |
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161 | // A can be converted to B |
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162 | template<int Phase, class A, class B> |
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163 | struct return_type_2_ifthenelsereturn<Phase, true, false, false, A, B> { |
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164 | typedef B type; |
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165 | }; |
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166 | |
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167 | // B can be converted to A |
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168 | template<int Phase, class A, class B> |
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169 | struct return_type_2_ifthenelsereturn<Phase, false, true, false, A, B> { |
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170 | typedef A type; |
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171 | }; |
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172 | |
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173 | // neither can be converted. Then we drop the potential references, and |
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174 | // try again |
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175 | template<class A, class B> |
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176 | struct return_type_2_ifthenelsereturn<1, false, false, false, A, B> { |
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177 | // it is safe to add const, since the result will be an rvalue and thus |
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178 | // const anyway. The const are needed eg. if the types |
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179 | // are 'const int*' and 'void *'. The remaining type should be 'const void*' |
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180 | typedef const typename boost::remove_reference<A>::type plainA; |
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181 | typedef const typename boost::remove_reference<B>::type plainB; |
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182 | // TODO: Add support for volatile ? |
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183 | |
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184 | typedef typename |
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185 | return_type_2_ifthenelsereturn< |
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186 | 2, |
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187 | boost::is_convertible<plainA,plainB>::value, |
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188 | boost::is_convertible<plainB,plainA>::value, |
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189 | boost::is_same<plainA,plainB>::value, |
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190 | plainA, |
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191 | plainB>::type type; |
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192 | }; |
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193 | |
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194 | // PHASE 6:2 |
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195 | template<class A, class B> |
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196 | struct return_type_2_ifthenelsereturn<2, false, false, false, A, B> { |
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197 | typedef |
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198 | detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type; |
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199 | // types_do_not_match_in_conditional_expression |
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200 | }; |
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201 | |
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202 | |
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203 | |
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204 | // PHASE 5: now we know that types are not arithmetic. |
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205 | template<class A, class B> |
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206 | struct non_numeric_types { |
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207 | typedef typename |
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208 | return_type_2_ifthenelsereturn< |
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209 | 1, // phase 1 |
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210 | is_convertible<A,B>::value, |
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211 | is_convertible<B,A>::value, |
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212 | is_same<A,B>::value, |
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213 | A, |
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214 | B>::type type; |
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215 | }; |
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216 | |
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217 | // PHASE 4 : |
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218 | // the base case covers arithmetic types with differing promote codes |
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219 | // use the type deduction of arithmetic_actions |
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220 | template<int CodeA, int CodeB, class A, class B> |
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221 | struct arithmetic_or_not { |
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222 | typedef typename |
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223 | return_type_2<arithmetic_action<plus_action>, A, B>::type type; |
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224 | // plus_action is just a random pick, has to be a concrete instance |
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225 | }; |
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226 | |
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227 | // this case covers the case of artihmetic types with the same promote codes. |
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228 | // non numeric deduction is used since e.g. integral promotion is not |
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229 | // performed with operator ?: |
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230 | template<int CodeA, class A, class B> |
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231 | struct arithmetic_or_not<CodeA, CodeA, A, B> { |
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232 | typedef typename non_numeric_types<A, B>::type type; |
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233 | }; |
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234 | |
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235 | // if either A or B has promote code -1 it is not an arithmetic type |
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236 | template<class A, class B> |
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237 | struct arithmetic_or_not <-1, -1, A, B> { |
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238 | typedef typename non_numeric_types<A, B>::type type; |
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239 | }; |
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240 | template<int CodeB, class A, class B> |
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241 | struct arithmetic_or_not <-1, CodeB, A, B> { |
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242 | typedef typename non_numeric_types<A, B>::type type; |
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243 | }; |
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244 | template<int CodeA, class A, class B> |
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245 | struct arithmetic_or_not <CodeA, -1, A, B> { |
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246 | typedef typename non_numeric_types<A, B>::type type; |
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247 | }; |
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248 | |
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249 | |
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250 | |
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251 | |
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252 | // PHASE 3 : Are the types same? |
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253 | // No, check if they are arithmetic or not |
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254 | template <class A, class B> |
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255 | struct same_or_not { |
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256 | typedef typename detail::remove_reference_and_cv<A>::type plainA; |
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257 | typedef typename detail::remove_reference_and_cv<B>::type plainB; |
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258 | |
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259 | typedef typename |
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260 | arithmetic_or_not< |
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261 | detail::promote_code<plainA>::value, |
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262 | detail::promote_code<plainB>::value, |
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263 | A, |
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264 | B>::type type; |
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265 | }; |
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266 | // Yes, clear. |
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267 | template <class A> struct same_or_not<A, A> { |
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268 | typedef A type; |
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269 | }; |
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270 | |
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271 | } // detail |
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272 | |
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273 | // PHASE 2 : Perform first the potential array_to_pointer conversion |
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274 | template<class A, class B> |
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275 | struct return_type_2<other_action<ifthenelsereturn_action>, A, B> { |
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276 | |
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277 | typedef typename detail::array_to_pointer<A>::type A1; |
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278 | typedef typename detail::array_to_pointer<B>::type B1; |
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279 | |
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280 | typedef typename |
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281 | boost::add_const<typename detail::same_or_not<A1, B1>::type>::type type; |
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282 | }; |
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283 | |
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284 | // PHASE 1 : Deduction is based on the second and third operand |
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285 | |
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286 | |
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287 | // return type specialization for conditional expression ends ----------- |
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288 | |
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289 | |
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290 | // Specialization of lambda_functor_base for if_then_else_return. |
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291 | template<class Args> |
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292 | class |
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293 | lambda_functor_base<other_action<ifthenelsereturn_action>, Args> { |
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294 | public: |
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295 | Args args; |
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296 | |
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297 | template <class SigArgs> struct sig { |
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298 | private: |
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299 | typedef typename detail::nth_return_type_sig<1, Args, SigArgs>::type ret1; |
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300 | typedef typename detail::nth_return_type_sig<2, Args, SigArgs>::type ret2; |
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301 | public: |
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302 | typedef typename return_type_2< |
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303 | other_action<ifthenelsereturn_action>, ret1, ret2 |
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304 | >::type type; |
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305 | }; |
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306 | |
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307 | public: |
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308 | explicit lambda_functor_base(const Args& a) : args(a) {} |
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309 | |
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310 | template<class RET, CALL_TEMPLATE_ARGS> |
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311 | RET call(CALL_FORMAL_ARGS) const { |
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312 | return (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) ? |
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313 | detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS) |
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314 | : |
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315 | detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS); |
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316 | } |
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317 | }; |
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318 | |
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319 | // The code below is from Joel de Guzman, some name changes etc. |
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320 | // has been made. |
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321 | |
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322 | /////////////////////////////////////////////////////////////////////////////// |
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323 | // |
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324 | // if_then_else_composite |
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325 | // |
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326 | // This composite has two (2) forms: |
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327 | // |
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328 | // if_(condition) |
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329 | // [ |
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330 | // statement |
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331 | // ] |
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332 | // |
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333 | // and |
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334 | // |
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335 | // if_(condition) |
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336 | // [ |
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337 | // true_statement |
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338 | // ] |
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339 | // .else_ |
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340 | // [ |
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341 | // false_statement |
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342 | // ] |
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343 | // |
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344 | // where condition is an lambda_functor that evaluates to bool. If condition |
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345 | // is true, the true_statement (again an lambda_functor) is executed |
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346 | // otherwise, the false_statement (another lambda_functor) is executed. The |
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347 | // result type of this is void. Note the trailing underscore after |
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348 | // if_ and the the leading dot and the trailing underscore before |
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349 | // and after .else_. |
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350 | // |
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351 | /////////////////////////////////////////////////////////////////////////////// |
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352 | template <typename CondT, typename ThenT, typename ElseT> |
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353 | struct if_then_else_composite { |
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354 | |
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355 | typedef if_then_else_composite<CondT, ThenT, ElseT> self_t; |
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356 | |
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357 | template <class SigArgs> |
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358 | struct sig { typedef void type; }; |
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359 | |
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360 | if_then_else_composite( |
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361 | CondT const& cond_, |
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362 | ThenT const& then_, |
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363 | ElseT const& else__) |
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364 | : cond(cond_), then(then_), else_(else__) {} |
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365 | |
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366 | template <class Ret, CALL_TEMPLATE_ARGS> |
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367 | Ret call(CALL_FORMAL_ARGS) const |
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368 | { |
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369 | if (cond.internal_call(CALL_ACTUAL_ARGS)) |
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370 | then.internal_call(CALL_ACTUAL_ARGS); |
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371 | else |
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372 | else_.internal_call(CALL_ACTUAL_ARGS); |
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373 | } |
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374 | |
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375 | CondT cond; ThenT then; ElseT else_; // lambda_functors |
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376 | }; |
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377 | |
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378 | ////////////////////////////////// |
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379 | template <typename CondT, typename ThenT> |
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380 | struct else_gen { |
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381 | |
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382 | else_gen(CondT const& cond_, ThenT const& then_) |
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383 | : cond(cond_), then(then_) {} |
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384 | |
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385 | template <typename ElseT> |
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386 | lambda_functor<if_then_else_composite<CondT, ThenT, |
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387 | typename as_lambda_functor<ElseT>::type> > |
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388 | operator[](ElseT const& else_) |
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389 | { |
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390 | typedef if_then_else_composite<CondT, ThenT, |
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391 | typename as_lambda_functor<ElseT>::type> |
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392 | result; |
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393 | |
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394 | return result(cond, then, to_lambda_functor(else_)); |
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395 | } |
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396 | |
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397 | CondT cond; ThenT then; |
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398 | }; |
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399 | |
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400 | ////////////////////////////////// |
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401 | template <typename CondT, typename ThenT> |
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402 | struct if_then_composite { |
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403 | |
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404 | template <class SigArgs> |
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405 | struct sig { typedef void type; }; |
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406 | |
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407 | if_then_composite(CondT const& cond_, ThenT const& then_) |
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408 | : cond(cond_), then(then_), else_(cond, then) {} |
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409 | |
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410 | template <class Ret, CALL_TEMPLATE_ARGS> |
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411 | Ret call(CALL_FORMAL_ARGS) const |
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412 | { |
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413 | if (cond.internal_call(CALL_ACTUAL_ARGS)) |
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414 | then.internal_call(CALL_ACTUAL_ARGS); |
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415 | } |
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416 | |
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417 | CondT cond; ThenT then; // lambda_functors |
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418 | else_gen<CondT, ThenT> else_; |
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419 | }; |
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420 | |
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421 | ////////////////////////////////// |
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422 | template <typename CondT> |
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423 | struct if_gen { |
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424 | |
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425 | if_gen(CondT const& cond_) |
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426 | : cond(cond_) {} |
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427 | |
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428 | template <typename ThenT> |
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429 | lambda_functor<if_then_composite< |
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430 | typename as_lambda_functor<CondT>::type, |
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431 | typename as_lambda_functor<ThenT>::type> > |
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432 | operator[](ThenT const& then) const |
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433 | { |
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434 | typedef if_then_composite< |
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435 | typename as_lambda_functor<CondT>::type, |
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436 | typename as_lambda_functor<ThenT>::type> |
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437 | result; |
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438 | |
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439 | return result( |
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440 | to_lambda_functor(cond), |
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441 | to_lambda_functor(then)); |
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442 | } |
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443 | |
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444 | CondT cond; |
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445 | }; |
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446 | |
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447 | ////////////////////////////////// |
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448 | template <typename CondT> |
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449 | inline if_gen<CondT> |
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450 | if_(CondT const& cond) |
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451 | { |
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452 | return if_gen<CondT>(cond); |
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453 | } |
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454 | |
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455 | |
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456 | |
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457 | } // lambda |
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458 | } // boost |
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459 | |
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460 | #endif // BOOST_LAMBDA_IF_HPP |
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461 | |
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462 | |
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