1 | // Boost Lambda Library ret.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 | // |
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5 | // Distributed under the Boost Software License, Version 1.0. (See |
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6 | // accompanying file LICENSE_1_0.txt or copy at |
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7 | // http://www.boost.org/LICENSE_1_0.txt) |
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8 | // |
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9 | // For more information, see www.boost.org |
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10 | |
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11 | |
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12 | #ifndef BOOST_LAMBDA_RET_HPP |
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13 | #define BOOST_LAMBDA_RET_HPP |
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14 | |
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15 | namespace boost { |
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16 | namespace lambda { |
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17 | |
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18 | // TODO: |
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19 | |
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20 | // Add specializations for function references for ret, protect and unlambda |
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21 | // e.g void foo(); unlambda(foo); fails, as it would add a const qualifier |
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22 | // for a function type. |
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23 | // on the other hand unlambda(*foo) does work |
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24 | |
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25 | |
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26 | // -- ret ------------------------- |
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27 | // the explicit return type template |
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28 | |
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29 | // TODO: It'd be nice to make ret a nop for other than lambda functors |
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30 | // but causes an ambiguiyty with gcc (not with KCC), check what is the |
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31 | // right interpretation. |
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32 | |
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33 | // // ret for others than lambda functors has no effect |
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34 | // template <class U, class T> |
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35 | // inline const T& ret(const T& t) { return t; } |
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36 | |
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37 | |
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38 | template<class RET, class Arg> |
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39 | inline const |
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40 | lambda_functor< |
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41 | lambda_functor_base< |
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42 | explicit_return_type_action<RET>, |
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43 | tuple<lambda_functor<Arg> > |
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44 | > |
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45 | > |
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46 | ret(const lambda_functor<Arg>& a1) |
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47 | { |
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48 | return |
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49 | lambda_functor_base< |
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50 | explicit_return_type_action<RET>, |
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51 | tuple<lambda_functor<Arg> > |
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52 | > |
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53 | (tuple<lambda_functor<Arg> >(a1)); |
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54 | } |
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55 | |
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56 | // protect ------------------ |
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57 | |
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58 | // protecting others than lambda functors has no effect |
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59 | template <class T> |
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60 | inline const T& protect(const T& t) { return t; } |
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61 | |
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62 | template<class Arg> |
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63 | inline const |
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64 | lambda_functor< |
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65 | lambda_functor_base< |
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66 | protect_action, |
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67 | tuple<lambda_functor<Arg> > |
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68 | > |
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69 | > |
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70 | protect(const lambda_functor<Arg>& a1) |
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71 | { |
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72 | return |
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73 | lambda_functor_base< |
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74 | protect_action, |
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75 | tuple<lambda_functor<Arg> > |
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76 | > |
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77 | (tuple<lambda_functor<Arg> >(a1)); |
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78 | } |
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79 | |
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80 | // ------------------------------------------------------------------- |
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81 | |
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82 | // Hides the lambda functorness of a lambda functor. |
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83 | // After this, the functor is immune to argument substitution, etc. |
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84 | // This can be used, e.g. to make it safe to pass lambda functors as |
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85 | // arguments to functions, which might use them as target functions |
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86 | |
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87 | // note, unlambda and protect are different things. Protect hides the lambda |
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88 | // functor for one application, unlambda for good. |
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89 | |
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90 | template <class LambdaFunctor> |
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91 | class non_lambda_functor |
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92 | { |
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93 | LambdaFunctor lf; |
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94 | public: |
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95 | |
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96 | // This functor defines the result_type typedef. |
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97 | // The result type must be deducible without knowing the arguments |
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98 | |
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99 | template <class SigArgs> struct sig { |
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100 | typedef typename |
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101 | LambdaFunctor::inherited:: |
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102 | template sig<typename SigArgs::tail_type>::type type; |
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103 | }; |
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104 | |
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105 | explicit non_lambda_functor(const LambdaFunctor& a) : lf(a) {} |
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106 | |
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107 | typename LambdaFunctor::nullary_return_type |
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108 | operator()() const { |
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109 | return lf.template |
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110 | call<typename LambdaFunctor::nullary_return_type> |
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111 | (cnull_type(), cnull_type(), cnull_type(), cnull_type()); |
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112 | } |
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113 | |
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114 | template<class A> |
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115 | typename sig<tuple<const non_lambda_functor, A&> >::type |
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116 | operator()(A& a) const { |
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117 | return lf.template call<typename sig<tuple<const non_lambda_functor, A&> >::type >(a, cnull_type(), cnull_type(), cnull_type()); |
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118 | } |
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119 | |
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120 | template<class A, class B> |
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121 | typename sig<tuple<const non_lambda_functor, A&, B&> >::type |
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122 | operator()(A& a, B& b) const { |
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123 | return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&> >::type >(a, b, cnull_type(), cnull_type()); |
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124 | } |
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125 | |
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126 | template<class A, class B, class C> |
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127 | typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type |
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128 | operator()(A& a, B& b, C& c) const { |
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129 | return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type>(a, b, c, cnull_type()); |
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130 | } |
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131 | }; |
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132 | |
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133 | template <class Arg> |
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134 | inline const Arg& unlambda(const Arg& a) { return a; } |
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135 | |
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136 | template <class Arg> |
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137 | inline const non_lambda_functor<lambda_functor<Arg> > |
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138 | unlambda(const lambda_functor<Arg>& a) |
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139 | { |
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140 | return non_lambda_functor<lambda_functor<Arg> >(a); |
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141 | } |
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142 | |
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143 | // Due to a language restriction, lambda functors cannot be made to |
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144 | // accept non-const rvalue arguments. Usually iterators do not return |
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145 | // temporaries, but sometimes they do. That's why a workaround is provided. |
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146 | // Note, that this potentially breaks const correctness, so be careful! |
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147 | |
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148 | // any lambda functor can be turned into a const_incorrect_lambda_functor |
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149 | // The operator() takes arguments as consts and then casts constness |
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150 | // away. So this breaks const correctness!!! but is a necessary workaround |
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151 | // in some cases due to language limitations. |
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152 | // Note, that this is not a lambda_functor anymore, so it can not be used |
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153 | // as a sub lambda expression. |
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154 | |
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155 | template <class LambdaFunctor> |
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156 | struct const_incorrect_lambda_functor { |
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157 | LambdaFunctor lf; |
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158 | public: |
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159 | |
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160 | explicit const_incorrect_lambda_functor(const LambdaFunctor& a) : lf(a) {} |
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161 | |
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162 | template <class SigArgs> struct sig { |
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163 | typedef typename |
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164 | LambdaFunctor::inherited::template |
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165 | sig<typename SigArgs::tail_type>::type type; |
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166 | }; |
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167 | |
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168 | // The nullary case is not needed (no arguments, no parameter type problems) |
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169 | |
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170 | template<class A> |
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171 | typename sig<tuple<const const_incorrect_lambda_functor, A&> >::type |
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172 | operator()(const A& a) const { |
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173 | return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&> >::type >(const_cast<A&>(a), cnull_type(), cnull_type(), cnull_type()); |
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174 | } |
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175 | |
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176 | template<class A, class B> |
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177 | typename sig<tuple<const const_incorrect_lambda_functor, A&, B&> >::type |
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178 | operator()(const A& a, const B& b) const { |
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179 | return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&, B&> >::type >(const_cast<A&>(a), const_cast<B&>(b), cnull_type(), cnull_type()); |
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180 | } |
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181 | |
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182 | template<class A, class B, class C> |
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183 | typename sig<tuple<const const_incorrect_lambda_functor, A&, B&, C&> >::type |
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184 | operator()(const A& a, const B& b, const C& c) const { |
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185 | return lf.template call<typename sig<tuple<const const_incorrect_lambda_functor, A&, B&, C&> >::type>(const_cast<A&>(a), const_cast<B&>(b), const_cast<C&>(c), cnull_type()); |
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186 | } |
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187 | }; |
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188 | |
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189 | // ------------------------------------------------------------------------ |
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190 | // any lambda functor can be turned into a const_parameter_lambda_functor |
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191 | // The operator() takes arguments as const. |
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192 | // This is useful if lambda functors are called with non-const rvalues. |
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193 | // Note, that this is not a lambda_functor anymore, so it can not be used |
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194 | // as a sub lambda expression. |
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195 | |
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196 | template <class LambdaFunctor> |
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197 | struct const_parameter_lambda_functor { |
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198 | LambdaFunctor lf; |
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199 | public: |
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200 | |
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201 | explicit const_parameter_lambda_functor(const LambdaFunctor& a) : lf(a) {} |
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202 | |
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203 | template <class SigArgs> struct sig { |
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204 | typedef typename |
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205 | LambdaFunctor::inherited::template |
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206 | sig<typename SigArgs::tail_type>::type type; |
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207 | }; |
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208 | |
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209 | // The nullary case is not needed: no arguments, no constness problems. |
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210 | |
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211 | template<class A> |
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212 | typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type |
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213 | operator()(const A& a) const { |
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214 | return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type >(a, cnull_type(), cnull_type(), cnull_type()); |
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215 | } |
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216 | |
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217 | template<class A, class B> |
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218 | typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type |
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219 | operator()(const A& a, const B& b) const { |
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220 | return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type >(a, b, cnull_type(), cnull_type()); |
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221 | } |
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222 | |
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223 | template<class A, class B, class C> |
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224 | typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&, const C&> |
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225 | >::type |
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226 | operator()(const A& a, const B& b, const C& c) const { |
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227 | return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&, const C&> >::type>(a, b, c, cnull_type()); |
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228 | } |
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229 | }; |
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230 | |
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231 | template <class Arg> |
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232 | inline const const_incorrect_lambda_functor<lambda_functor<Arg> > |
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233 | break_const(const lambda_functor<Arg>& lf) |
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234 | { |
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235 | return const_incorrect_lambda_functor<lambda_functor<Arg> >(lf); |
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236 | } |
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237 | |
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238 | |
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239 | template <class Arg> |
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240 | inline const const_parameter_lambda_functor<lambda_functor<Arg> > |
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241 | const_parameters(const lambda_functor<Arg>& lf) |
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242 | { |
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243 | return const_parameter_lambda_functor<lambda_functor<Arg> >(lf); |
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244 | } |
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245 | |
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246 | // make void ------------------------------------------------ |
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247 | // make_void( x ) turns a lambda functor x with some return type y into |
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248 | // another lambda functor, which has a void return type |
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249 | // when called, the original return type is discarded |
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250 | |
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251 | // we use this action. The action class will be called, which means that |
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252 | // the wrapped lambda functor is evaluated, but we just don't do anything |
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253 | // with the result. |
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254 | struct voidifier_action { |
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255 | template<class Ret, class A> static void apply(A&) {} |
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256 | }; |
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257 | |
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258 | template<class Args> struct return_type_N<voidifier_action, Args> { |
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259 | typedef void type; |
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260 | }; |
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261 | |
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262 | template<class Arg1> |
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263 | inline const |
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264 | lambda_functor< |
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265 | lambda_functor_base< |
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266 | action<1, voidifier_action>, |
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267 | tuple<lambda_functor<Arg1> > |
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268 | > |
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269 | > |
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270 | make_void(const lambda_functor<Arg1>& a1) { |
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271 | return |
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272 | lambda_functor_base< |
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273 | action<1, voidifier_action>, |
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274 | tuple<lambda_functor<Arg1> > |
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275 | > |
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276 | (tuple<lambda_functor<Arg1> > (a1)); |
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277 | } |
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278 | |
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279 | // for non-lambda functors, make_void does nothing |
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280 | // (the argument gets evaluated immediately) |
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281 | |
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282 | template<class Arg1> |
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283 | inline const |
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284 | lambda_functor< |
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285 | lambda_functor_base<do_nothing_action, null_type> |
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286 | > |
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287 | make_void(const Arg1& a1) { |
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288 | return |
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289 | lambda_functor_base<do_nothing_action, null_type>(); |
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290 | } |
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291 | |
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292 | // std_functor ----------------------------------------------------- |
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293 | |
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294 | // The STL uses the result_type typedef as the convention to let binders know |
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295 | // the return type of a function object. |
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296 | // LL uses the sig template. |
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297 | // To let LL know that the function object has the result_type typedef |
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298 | // defined, it can be wrapped with the std_functor function. |
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299 | |
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300 | |
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301 | // Just inherit form the template parameter (the standard functor), |
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302 | // and provide a sig template. So we have a class which is still the |
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303 | // same functor + the sig template. |
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304 | |
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305 | template<class T> |
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306 | struct result_type_to_sig : public T { |
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307 | template<class Args> struct sig { typedef typename T::result_type type; }; |
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308 | result_type_to_sig(const T& t) : T(t) {} |
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309 | }; |
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310 | |
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311 | template<class F> |
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312 | inline result_type_to_sig<F> std_functor(const F& f) { return f; } |
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313 | |
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314 | |
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315 | } // namespace lambda |
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316 | } // namespace boost |
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317 | |
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318 | #endif |
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319 | |
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320 | |
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321 | |
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322 | |
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323 | |
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324 | |
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325 | |
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