Symaptic: os/ossrv/ossrv_pub/boost_apis/boost/lambda/if.hpp@bde4ae8d615e

     1 // Boost Lambda Library -- if.hpp ------------------------------------------

     3 // Copyright (C) 1999, 2000 Jaakko Järvi (jaakko.jarvi@cs.utu.fi)

     4 // Copyright (C) 2000 Gary Powell (powellg@amazon.com)

     5 // Copyright (C) 2001-2002 Joel de Guzman

     6 //

     7 // Distributed under the Boost Software License, Version 1.0. (See

     8 // accompanying file LICENSE_1_0.txt or copy at

     9 // http://www.boost.org/LICENSE_1_0.txt)

    10 //

    11 // For more information, see www.boost.org

    13 // --------------------------------------------------------------------------

    15 #if !defined(BOOST_LAMBDA_IF_HPP)

    16 #define BOOST_LAMBDA_IF_HPP

    18 #include "boost/lambda/core.hpp"

    20 // Arithmetic type promotion needed for if_then_else_return

    21 #include "boost/lambda/detail/operator_actions.hpp"

    22 #include "boost/lambda/detail/operator_return_type_traits.hpp"

    24 namespace boost {

    25 namespace lambda {

    27 // -- if control construct actions ----------------------

    29 class ifthen_action {};

    30 class ifthenelse_action {};

    31 class ifthenelsereturn_action {};

    33 // Specialization for if_then.

    34 template<class Args>

    35 class

    36 lambda_functor_base<ifthen_action, Args> {

    37 public:

    38   Args args;

    39   template <class T> struct sig { typedef void type; };

    40 public:

    41   explicit lambda_functor_base(const Args& a) : args(a) {}

    43   template<class RET, CALL_TEMPLATE_ARGS>

    44   RET call(CALL_FORMAL_ARGS) const {

    45     if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS))

    46       detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS);

    47   }

    48 };

    50 // If Then

    51 template <class Arg1, class Arg2>

    52 inline const

    53 lambda_functor<

    54   lambda_functor_base<

    55     ifthen_action,

    56     tuple<lambda_functor<Arg1>, lambda_functor<Arg2> >

    57   >

    58 >

    59 if_then(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2) {

    60   return

    61     lambda_functor_base<

    62       ifthen_action,

    63       tuple<lambda_functor<Arg1>, lambda_functor<Arg2> >

    64     >

    65     ( tuple<lambda_functor<Arg1>, lambda_functor<Arg2> >(a1, a2) );

    66 }

    69 // Specialization for if_then_else.

    70 template<class Args>

    71 class

    72 lambda_functor_base<ifthenelse_action, Args> {

    73 public:

    74   Args args;

    75   template <class T> struct sig { typedef void type; };

    76 public:

    77   explicit lambda_functor_base(const Args& a) : args(a) {}

    79   template<class RET, CALL_TEMPLATE_ARGS>

    80   RET call(CALL_FORMAL_ARGS) const {

    81     if (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS))

    82       detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS);

    83     else

    84       detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS);

    85   }

    86 };

    90 // If then else

    92 template <class Arg1, class Arg2, class Arg3>

    93 inline const

    94 lambda_functor<

    95   lambda_functor_base<

    96     ifthenelse_action,

    97     tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> >

    98   >

    99 >

   100 if_then_else(const lambda_functor<Arg1>& a1, const lambda_functor<Arg2>& a2,

   101              const lambda_functor<Arg3>& a3) {

   102   return

   103     lambda_functor_base<

   104       ifthenelse_action,

   105       tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> >

   106     >

   107     (tuple<lambda_functor<Arg1>, lambda_functor<Arg2>, lambda_functor<Arg3> >

   108        (a1, a2, a3) );

   109 }

   111 // Our version of operator?:()

   113 template <class Arg1, class Arg2, class Arg3>

   114 inline const

   115   lambda_functor<

   116     lambda_functor_base<

   117       other_action<ifthenelsereturn_action>,

   118       tuple<lambda_functor<Arg1>,

   119           typename const_copy_argument<Arg2>::type,

   120           typename const_copy_argument<Arg3>::type>

   121   >

   122 >

   123 if_then_else_return(const lambda_functor<Arg1>& a1,

   124                     const Arg2 & a2,

   125                     const Arg3 & a3) {

   126   return

   127       lambda_functor_base<

   128         other_action<ifthenelsereturn_action>,

   129         tuple<lambda_functor<Arg1>,

   130               typename const_copy_argument<Arg2>::type,

   131               typename const_copy_argument<Arg3>::type>

   132       > ( tuple<lambda_functor<Arg1>,

   133               typename const_copy_argument<Arg2>::type,

   134               typename const_copy_argument<Arg3>::type> (a1, a2, a3) );

   135 }

   137 namespace detail {

   139 // return type specialization for conditional expression begins -----------

   140 // start reading below and move upwards

   142 // PHASE 6:1

   143 // check if A is conbertible to B and B to A

   144 template<int Phase, bool AtoB, bool BtoA, bool SameType, class A, class B>

   145 struct return_type_2_ifthenelsereturn;

   147 // if A can be converted to B and vice versa -> ambiguous

   148 template<int Phase, class A, class B>

   149 struct return_type_2_ifthenelsereturn<Phase, true, true, false, A, B> {

   150   typedef

   151     detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type;

   152   // ambiguous type in conditional expression

   153 };

   154 // if A can be converted to B and vice versa and are of same type

   155 template<int Phase, class A, class B>

   156 struct return_type_2_ifthenelsereturn<Phase, true, true, true, A, B> {

   157   typedef A type;

   158 };

   161 // A can be converted to B

   162 template<int Phase, class A, class B>

   163 struct return_type_2_ifthenelsereturn<Phase, true, false, false, A, B> {

   164   typedef B type;

   165 };

   167 // B can be converted to A

   168 template<int Phase, class A, class B>

   169 struct return_type_2_ifthenelsereturn<Phase, false, true, false, A, B> {

   170   typedef A type;

   171 };

   173 // neither can be converted. Then we drop the potential references, and

   174 // try again

   175 template<class A, class B>

   176 struct return_type_2_ifthenelsereturn<1, false, false, false, A, B> {

   177   // it is safe to add const, since the result will be an rvalue and thus

   178   // const anyway. The const are needed eg. if the types

   179   // are 'const int*' and 'void *'. The remaining type should be 'const void*'

   180   typedef const typename boost::remove_reference<A>::type plainA;

   181   typedef const typename boost::remove_reference<B>::type plainB;

   182   // TODO: Add support for volatile ?

   184   typedef typename

   185        return_type_2_ifthenelsereturn<

   186          2,

   187          boost::is_convertible<plainA,plainB>::value,

   188          boost::is_convertible<plainB,plainA>::value,

   189          boost::is_same<plainA,plainB>::value,

   190          plainA,

   191          plainB>::type type;

   192 };

   194 // PHASE 6:2

   195 template<class A, class B>

   196 struct return_type_2_ifthenelsereturn<2, false, false, false, A, B> {

   197   typedef

   198     detail::return_type_deduction_failure<return_type_2_ifthenelsereturn> type;

   199   // types_do_not_match_in_conditional_expression

   200 };

   204 // PHASE 5: now we know that types are not arithmetic.

   205 template<class A, class B>

   206 struct non_numeric_types {

   207   typedef typename

   208     return_type_2_ifthenelsereturn<

   209       1, // phase 1

   210       is_convertible<A,B>::value,

   211       is_convertible<B,A>::value,

   212       is_same<A,B>::value,

   213       A,

   214       B>::type type;

   215 };

   217 // PHASE 4 :

   218 // the base case covers arithmetic types with differing promote codes

   219 // use the type deduction of arithmetic_actions

   220 template<int CodeA, int CodeB, class A, class B>

   221 struct arithmetic_or_not {

   222   typedef typename

   223     return_type_2<arithmetic_action<plus_action>, A, B>::type type;

   224   // plus_action is just a random pick, has to be a concrete instance

   225 };

   227 // this case covers the case of artihmetic types with the same promote codes.

   228 // non numeric deduction is used since e.g. integral promotion is not

   229 // performed with operator ?:

   230 template<int CodeA, class A, class B>

   231 struct arithmetic_or_not<CodeA, CodeA, A, B> {

   232   typedef typename non_numeric_types<A, B>::type type;

   233 };

   235 // if either A or B has promote code -1 it is not an arithmetic type

   236 template<class A, class B>

   237 struct arithmetic_or_not <-1, -1, A, B> {

   238   typedef typename non_numeric_types<A, B>::type type;

   239 };

   240 template<int CodeB, class A, class B>

   241 struct arithmetic_or_not <-1, CodeB, A, B> {

   242   typedef typename non_numeric_types<A, B>::type type;

   243 };

   244 template<int CodeA, class A, class B>

   245 struct arithmetic_or_not <CodeA, -1, A, B> {

   246   typedef typename non_numeric_types<A, B>::type type;

   247 };

   252 // PHASE 3 : Are the types same?

   253 // No, check if they are arithmetic or not

   254 template <class A, class B>

   255 struct same_or_not {

   256   typedef typename detail::remove_reference_and_cv<A>::type plainA;

   257   typedef typename detail::remove_reference_and_cv<B>::type plainB;

   259   typedef typename

   260     arithmetic_or_not<

   261       detail::promote_code<plainA>::value,

   262       detail::promote_code<plainB>::value,

   263       A,

   264       B>::type type;

   265 };

   266 // Yes, clear.

   267 template <class A> struct same_or_not<A, A> {

   268   typedef A type;

   269 };

   271 } // detail

   273 // PHASE 2 : Perform first the potential array_to_pointer conversion

   274 template<class A, class B>

   275 struct return_type_2<other_action<ifthenelsereturn_action>, A, B> {

   277   typedef typename detail::array_to_pointer<A>::type A1;

   278   typedef typename detail::array_to_pointer<B>::type B1;

   280   typedef typename

   281     boost::add_const<typename detail::same_or_not<A1, B1>::type>::type type;

   282 };

   284 // PHASE 1 : Deduction is based on the second and third operand

   287 // return type specialization for conditional expression ends -----------

   290 // Specialization of lambda_functor_base for if_then_else_return.

   291 template<class Args>

   292 class

   293 lambda_functor_base<other_action<ifthenelsereturn_action>, Args> {

   294 public:

   295   Args args;

   297   template <class SigArgs> struct sig {

   298   private:

   299     typedef typename detail::nth_return_type_sig<1, Args, SigArgs>::type ret1;

   300     typedef typename detail::nth_return_type_sig<2, Args, SigArgs>::type ret2;

   301   public:

   302     typedef typename return_type_2<

   303       other_action<ifthenelsereturn_action>, ret1, ret2

   304     >::type type;

   305   };

   307 public:

   308   explicit lambda_functor_base(const Args& a) : args(a) {}

   310   template<class RET, CALL_TEMPLATE_ARGS>

   311   RET call(CALL_FORMAL_ARGS) const {

   312     return (detail::select(boost::tuples::get<0>(args), CALL_ACTUAL_ARGS)) ?

   313        detail::select(boost::tuples::get<1>(args), CALL_ACTUAL_ARGS)

   314     :

   315        detail::select(boost::tuples::get<2>(args), CALL_ACTUAL_ARGS);

   316   }

   317 };

   319   // The code below is from Joel de Guzman, some name changes etc.

   320   // has been made.

   322 ///////////////////////////////////////////////////////////////////////////////

   323 //

   324 //  if_then_else_composite

   325 //

   326 //      This composite has two (2) forms:

   327 //

   328 //          if_(condition)

   329 //          [

   330 //              statement

   331 //          ]

   332 //

   333 //      and

   334 //

   335 //          if_(condition)

   336 //          [

   337 //              true_statement

   338 //          ]

   339 //          .else_

   340 //          [

   341 //              false_statement

   342 //          ]

   343 //

   344 //      where condition is an lambda_functor that evaluates to bool. If condition

   345 //      is true, the true_statement (again an lambda_functor) is executed

   346 //      otherwise, the false_statement (another lambda_functor) is executed. The

   347 //      result type of this is void. Note the trailing underscore after

   348 //      if_ and the the leading dot and the trailing underscore before

   349 //      and after .else_.

   350 //

   351 ///////////////////////////////////////////////////////////////////////////////

   352 template <typename CondT, typename ThenT, typename ElseT>

   353 struct if_then_else_composite {

   355     typedef if_then_else_composite<CondT, ThenT, ElseT> self_t;

   357     template <class SigArgs>

   358     struct sig { typedef void type; };

   360     if_then_else_composite(

   361         CondT const& cond_,

   362         ThenT const& then_,

   363         ElseT const& else__)

   364     :   cond(cond_), then(then_), else_(else__) {}

   366     template <class Ret, CALL_TEMPLATE_ARGS>

   367     Ret call(CALL_FORMAL_ARGS) const

   368     {

   369         if (cond.internal_call(CALL_ACTUAL_ARGS))

   370             then.internal_call(CALL_ACTUAL_ARGS);

   371         else

   372             else_.internal_call(CALL_ACTUAL_ARGS);

   373     }

   375     CondT cond; ThenT then; ElseT else_; //  lambda_functors

   376 };

   378 //////////////////////////////////

   379 template <typename CondT, typename ThenT>

   380 struct else_gen {

   382     else_gen(CondT const& cond_, ThenT const& then_)

   383     :   cond(cond_), then(then_) {}

   385     template <typename ElseT>

   386     lambda_functor<if_then_else_composite<CondT, ThenT,

   387         typename as_lambda_functor<ElseT>::type> >

   388     operator[](ElseT const& else_)

   389     {

   390         typedef if_then_else_composite<CondT, ThenT,

   391             typename as_lambda_functor<ElseT>::type>

   392         result;

   394         return result(cond, then, to_lambda_functor(else_));

   395     }

   397     CondT cond; ThenT then;

   398 };

   400 //////////////////////////////////

   401 template <typename CondT, typename ThenT>

   402 struct if_then_composite {

   404     template <class SigArgs>

   405     struct sig { typedef void type; };

   407     if_then_composite(CondT const& cond_, ThenT const& then_)

   408     :   cond(cond_), then(then_), else_(cond, then) {}

   410     template <class Ret, CALL_TEMPLATE_ARGS>

   411     Ret call(CALL_FORMAL_ARGS) const

   412     {

   413       if (cond.internal_call(CALL_ACTUAL_ARGS))

   414             then.internal_call(CALL_ACTUAL_ARGS);

   415     }

   417     CondT cond; ThenT then; //  lambda_functors

   418     else_gen<CondT, ThenT> else_;

   419 };

   421 //////////////////////////////////

   422 template <typename CondT>

   423 struct if_gen {

   425     if_gen(CondT const& cond_)

   426     :   cond(cond_) {}

   428     template <typename ThenT>

   429     lambda_functor<if_then_composite<

   430         typename as_lambda_functor<CondT>::type,

   431         typename as_lambda_functor<ThenT>::type> >

   432     operator[](ThenT const& then) const

   433     {

   434         typedef if_then_composite<

   435             typename as_lambda_functor<CondT>::type,

   436             typename as_lambda_functor<ThenT>::type>

   437         result;

   439         return result(

   440             to_lambda_functor(cond),

   441             to_lambda_functor(then));

   442     }

   444     CondT cond;

   445 };

   447 //////////////////////////////////

   448 template <typename CondT>

   449 inline if_gen<CondT>

   450 if_(CondT const& cond)

   451 {

   452     return if_gen<CondT>(cond);

   453 }

   457 } // lambda

   458 } // boost

   460 #endif // BOOST_LAMBDA_IF_HPP

author	sl@SLION-WIN7.fritz.box
	Fri, 15 Jun 2012 03:10:57 +0200
changeset 0	bde4ae8d615e
permissions	-rw-r--r--