boost/mpl/aux_/begin_end_impl.hpp

   1
   2 #ifndef BOOST_MPL_AUX_BEGIN_END_IMPL_HPP_INCLUDED
   3 #define BOOST_MPL_AUX_BEGIN_END_IMPL_HPP_INCLUDED
   4
   5 // Copyright Aleksey Gurtovoy 2000-2004
   6 //
   7 // Distributed under the Boost Software License, Version 1.0.
   8 // (See accompanying file LICENSE_1_0.txt or copy at
   9 // http://www.boost.org/LICENSE_1_0.txt)
  10 //
  11 // See http://www.boost.org/libs/mpl for documentation.
  12
  13 // $Id: begin_end_impl.hpp 49267 2008-10-11 06:19:02Z agurtovoy $
  14 // $Date: 2008-10-10 23:19:02 -0700 (Fri, 10 Oct 2008) $
  15 // $Revision: 49267 $
  16
  17 #include <boost/mpl/begin_end_fwd.hpp>
  18 #include <boost/mpl/sequence_tag_fwd.hpp>
  19 #include <boost/mpl/void.hpp>
  20 #include <boost/mpl/eval_if.hpp>
  21 #include <boost/mpl/aux_/has_begin.hpp>
  22 #include <boost/mpl/aux_/na.hpp>
  23 #include <boost/mpl/aux_/traits_lambda_spec.hpp>
  24 #include <boost/mpl/aux_/config/eti.hpp>
  25
  26 namespace boost { namespace mpl {
  27
  28
  29 namespace aux {
  30
  31 template< typename Sequence >
  32 struct begin_type
  33 {
  34     typedef typename Sequence::begin type;
  35 };
  36 template< typename Sequence >
  37 struct end_type
  38 {
  39     typedef typename Sequence::end type;
  40 };
  41
  42 }
  43
  44 // default implementation; conrete sequences might override it by
  45 // specializing either the 'begin_impl/end_impl' or the primary
  46 // 'begin/end' templates
  47
  48 template< typename Tag >
  49 struct begin_impl
  50 {
  51     template< typename Sequence > struct apply
  52     {
  53         typedef typename eval_if<aux::has_begin<Sequence, true_>,
  54                                  aux::begin_type<Sequence>, void_>::type type;
  55     };
  56 };
  57
  58 template< typename Tag >
  59 struct end_impl
  60 {
  61     template< typename Sequence > struct apply
  62     {
  63         typedef typename eval_if<aux::has_begin<Sequence, true_>,
  64                                  aux::end_type<Sequence>, void_>::type type;
  65     };
  66 };
  67
  68 // specialize 'begin_trait/end_trait' for two pre-defined tags
  69
  70 #   define AUX778076_IMPL_SPEC(name, tag, result) \
  71 template<> \
  72 struct name##_impl<tag> \
  73 { \
  74     template< typename Sequence > struct apply \
  75     { \
  76         typedef result type; \
  77     }; \
  78 }; \
  79 /**/
  80
  81 // a sequence with nested 'begin/end' typedefs; just query them
  82 AUX778076_IMPL_SPEC(begin, nested_begin_end_tag, typename Sequence::begin)
  83 AUX778076_IMPL_SPEC(end, nested_begin_end_tag, typename Sequence::end)
  84
  85 // if a type 'T' does not contain 'begin/end' or 'tag' members
  86 // and doesn't specialize either 'begin/end' or 'begin_impl/end_impl'
  87 // templates, then we end up here
  88 AUX778076_IMPL_SPEC(begin, non_sequence_tag, void_)
  89 AUX778076_IMPL_SPEC(end, non_sequence_tag, void_)
  90 AUX778076_IMPL_SPEC(begin, na, void_)
  91 AUX778076_IMPL_SPEC(end, na, void_)
  92
  93 #   undef AUX778076_IMPL_SPEC
  94
  95
  96 BOOST_MPL_ALGORITM_TRAITS_LAMBDA_SPEC_IMPL(1,begin_impl)
  97 BOOST_MPL_ALGORITM_TRAITS_LAMBDA_SPEC_IMPL(1,end_impl)
  98
  99 }}
 100
 101 #endif // BOOST_MPL_AUX_BEGIN_END_IMPL_HPP_INCLUDED