ceph/src/boost/libs/lambda/include/boost/lambda/detail/ret.hpp

   1 // Boost Lambda Library  ret.hpp -----------------------------------------
   2
   3 // Copyright (C) 1999, 2000 Jaakko Jarvi (jaakko.jarvi@cs.utu.fi)
   4 //
   5 // Distributed under the Boost Software License, Version 1.0. (See
   6 // accompanying file LICENSE_1_0.txt or copy at
   7 // http://www.boost.org/LICENSE_1_0.txt)
   8 //
   9 // For more information, see www.boost.org
  10
  11
  12 #ifndef BOOST_LAMBDA_RET_HPP
  13 #define BOOST_LAMBDA_RET_HPP
  14
  15 namespace boost {
  16 namespace lambda {
  17
  18   // TODO:
  19
  20 //  Add specializations for function references for ret, protect and unlambda
  21 //  e.g void foo(); unlambda(foo); fails, as it would add a const qualifier
  22   // for a function type.
  23   // on the other hand unlambda(*foo) does work
  24
  25
  26 // -- ret -------------------------
  27 // the explicit return type template
  28
  29   // TODO: It'd be nice to make ret a nop for other than lambda functors
  30   // but causes an ambiguiyty with gcc (not with KCC), check what is the
  31   // right interpretation.
  32
  33   //  // ret for others than lambda functors has no effect
  34   // template <class U, class T>
  35   // inline const T& ret(const T& t) { return t; }
  36
  37
  38 template<class RET, class Arg>
  39 inline const
  40 lambda_functor<
  41   lambda_functor_base<
  42     explicit_return_type_action<RET>,
  43     tuple<lambda_functor<Arg> >
  44   >
  45 >
  46 ret(const lambda_functor<Arg>& a1)
  47 {
  48   return
  49     lambda_functor_base<
  50       explicit_return_type_action<RET>,
  51       tuple<lambda_functor<Arg> >
  52     >
  53     (tuple<lambda_functor<Arg> >(a1));
  54 }
  55
  56 // protect ------------------
  57
  58   // protecting others than lambda functors has no effect
  59 template <class T>
  60 inline const T& protect(const T& t) { return t; }
  61
  62 template<class Arg>
  63 inline const
  64 lambda_functor<
  65   lambda_functor_base<
  66     protect_action,
  67     tuple<lambda_functor<Arg> >
  68   >
  69 >
  70 protect(const lambda_functor<Arg>& a1)
  71 {
  72   return
  73       lambda_functor_base<
  74         protect_action,
  75         tuple<lambda_functor<Arg> >
  76       >
  77     (tuple<lambda_functor<Arg> >(a1));
  78 }
  79
  80 // -------------------------------------------------------------------
  81
  82 // Hides the lambda functorness of a lambda functor.
  83 // After this, the functor is immune to argument substitution, etc.
  84 // This can be used, e.g. to make it safe to pass lambda functors as
  85 // arguments to functions, which might use them as target functions
  86
  87 // note, unlambda and protect are different things. Protect hides the lambda
  88 // functor for one application, unlambda for good.
  89
  90 template <class LambdaFunctor>
  91 class non_lambda_functor
  92 {
  93   LambdaFunctor lf;
  94 public:
  95
  96   // This functor defines the result_type typedef.
  97   // The result type must be deducible without knowing the arguments
  98
  99   template <class SigArgs> struct sig {
 100     typedef typename
 101       LambdaFunctor::inherited::
 102         template sig<typename SigArgs::tail_type>::type type;
 103   };
 104
 105   explicit non_lambda_functor(const LambdaFunctor& a) : lf(a) {}
 106
 107   typename LambdaFunctor::nullary_return_type
 108   operator()() const {
 109     return lf.template
 110       call<typename LambdaFunctor::nullary_return_type>
 111         (cnull_type(), cnull_type(), cnull_type(), cnull_type());
 112   }
 113
 114   template<class A>
 115   typename sig<tuple<const non_lambda_functor, A&> >::type
 116   operator()(A& a) const {
 117     return lf.template call<typename sig<tuple<const non_lambda_functor, A&> >::type >(a, cnull_type(), cnull_type(), cnull_type());
 118   }
 119
 120   template<class A, class B>
 121   typename sig<tuple<const non_lambda_functor, A&, B&> >::type
 122   operator()(A& a, B& b) const {
 123     return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&> >::type >(a, b, cnull_type(), cnull_type());
 124   }
 125
 126   template<class A, class B, class C>
 127   typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type
 128   operator()(A& a, B& b, C& c) const {
 129     return lf.template call<typename sig<tuple<const non_lambda_functor, A&, B&, C&> >::type>(a, b, c, cnull_type());
 130   }
 131 };
 132
 133 template <class Arg>
 134 inline const Arg& unlambda(const Arg& a) { return a; }
 135
 136 template <class Arg>
 137 inline const non_lambda_functor<lambda_functor<Arg> >
 138 unlambda(const lambda_functor<Arg>& a)
 139 {
 140   return non_lambda_functor<lambda_functor<Arg> >(a);
 141 }
 142
 143   // Due to a language restriction, lambda functors cannot be made to
 144   // accept non-const rvalue arguments. Usually iterators do not return
 145   // temporaries, but sometimes they do. That's why a workaround is provided.
 146   // Note, that this potentially breaks const correctness, so be careful!
 147
 148 // any lambda functor can be turned into a const_incorrect_lambda_functor
 149 // The operator() takes arguments as consts and then casts constness
 150 // away. So this breaks const correctness!!! but is a necessary workaround
 151 // in some cases due to language limitations.
 152 // Note, that this is not a lambda_functor anymore, so it can not be used
 153 // as a sub lambda expression.
 154
 155 template <class LambdaFunctor>
 156 struct const_incorrect_lambda_functor {
 157   LambdaFunctor lf;
 158 public:
 159
 160   explicit const_incorrect_lambda_functor(const LambdaFunctor& a) : lf(a) {}
 161
 162   template <class SigArgs> struct sig {
 163     typedef typename
 164       LambdaFunctor::inherited::template
 165         sig<typename SigArgs::tail_type>::type type;
 166   };
 167
 168   // The nullary case is not needed (no arguments, no parameter type problems)
 169
 170   template<class A>
 171   typename sig<tuple<const const_incorrect_lambda_functor, A&> >::type
 172   operator()(const A& a) const {
 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());
 174   }
 175
 176   template<class A, class B>
 177   typename sig<tuple<const const_incorrect_lambda_functor, A&, B&> >::type
 178   operator()(const A& a, const B& b) const {
 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());
 180   }
 181
 182   template<class A, class B, class C>
 183   typename sig<tuple<const const_incorrect_lambda_functor, A&, B&, C&> >::type
 184   operator()(const A& a, const B& b, const C& c) const {
 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());
 186   }
 187 };
 188
 189 // ------------------------------------------------------------------------
 190 // any lambda functor can be turned into a const_parameter_lambda_functor
 191 // The operator() takes arguments as const.
 192 // This is useful if lambda functors are called with non-const rvalues.
 193 // Note, that this is not a lambda_functor anymore, so it can not be used
 194 // as a sub lambda expression.
 195
 196 template <class LambdaFunctor>
 197 struct const_parameter_lambda_functor {
 198   LambdaFunctor lf;
 199 public:
 200
 201   explicit const_parameter_lambda_functor(const LambdaFunctor& a) : lf(a) {}
 202
 203   template <class SigArgs> struct sig {
 204     typedef typename
 205       LambdaFunctor::inherited::template
 206         sig<typename SigArgs::tail_type>::type type;
 207   };
 208
 209   // The nullary case is not needed: no arguments, no constness problems.
 210
 211   template<class A>
 212   typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type
 213   operator()(const A& a) const {
 214     return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&> >::type >(a, cnull_type(), cnull_type(), cnull_type());
 215   }
 216
 217   template<class A, class B>
 218   typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type
 219   operator()(const A& a, const B& b) const {
 220     return lf.template call<typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&> >::type >(a, b, cnull_type(), cnull_type());
 221   }
 222
 223   template<class A, class B, class C>
 224   typename sig<tuple<const const_parameter_lambda_functor, const A&, const B&, const C&>
 225 >::type
 226   operator()(const A& a, const B& b, const C& c) const {
 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());
 228   }
 229 };
 230
 231 template <class Arg>
 232 inline const const_incorrect_lambda_functor<lambda_functor<Arg> >
 233 break_const(const lambda_functor<Arg>& lf)
 234 {
 235   return const_incorrect_lambda_functor<lambda_functor<Arg> >(lf);
 236 }
 237
 238
 239 template <class Arg>
 240 inline const const_parameter_lambda_functor<lambda_functor<Arg> >
 241 const_parameters(const lambda_functor<Arg>& lf)
 242 {
 243   return const_parameter_lambda_functor<lambda_functor<Arg> >(lf);
 244 }
 245
 246 // make void ------------------------------------------------
 247 // make_void( x ) turns a lambda functor x with some return type y into
 248 // another lambda functor, which has a void return type
 249 // when called, the original return type is discarded
 250
 251 // we use this action. The action class will be called, which means that
 252 // the wrapped lambda functor is evaluated, but we just don't do anything
 253 // with the result.
 254 struct voidifier_action {
 255   template<class Ret, class A> static void apply(A&) {}
 256 };
 257
 258 template<class Args> struct return_type_N<voidifier_action, Args> {
 259   typedef void type;
 260 };
 261
 262 template<class Arg1>
 263 inline const
 264 lambda_functor<
 265   lambda_functor_base<
 266     action<1, voidifier_action>,
 267     tuple<lambda_functor<Arg1> >
 268   >
 269 >
 270 make_void(const lambda_functor<Arg1>& a1) {
 271 return
 272     lambda_functor_base<
 273       action<1, voidifier_action>,
 274       tuple<lambda_functor<Arg1> >
 275     >
 276   (tuple<lambda_functor<Arg1> > (a1));
 277 }
 278
 279 // for non-lambda functors, make_void does nothing
 280 // (the argument gets evaluated immediately)
 281
 282 template<class Arg1>
 283 inline const
 284 lambda_functor<
 285   lambda_functor_base<do_nothing_action, null_type>
 286 >
 287 make_void(const Arg1&) {
 288 return
 289     lambda_functor_base<do_nothing_action, null_type>();
 290 }
 291
 292 // std_functor -----------------------------------------------------
 293
 294 //  The STL uses the result_type typedef as the convention to let binders know
 295 //  the return type of a function object.
 296 //  LL uses the sig template.
 297 //  To let LL know that the function object has the result_type typedef
 298 //  defined, it can be wrapped with the std_functor function.
 299
 300
 301 // Just inherit form the template parameter (the standard functor),
 302 // and provide a sig template. So we have a class which is still the
 303 // same functor + the sig template.
 304
 305 template<class T>
 306 struct result_type_to_sig : public T {
 307   template<class Args> struct sig { typedef typename T::result_type type; };
 308   result_type_to_sig(const T& t) : T(t) {}
 309 };
 310
 311 template<class F>
 312 inline result_type_to_sig<F> std_functor(const F& f) { return f; }
 313
 314
 315 } // namespace lambda
 316 } // namespace boost
 317
 318 #endif
 319
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