ceph/src/boost/libs/parameter/include/boost/parameter/value_type.hpp

   1 // Copyright Daniel Wallin 2006. Use, modification and distribution is
   2 // subject to the Boost Software License, Version 1.0. (See accompanying
   3 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
   4
   5 #ifndef BOOST_PARAMETER_VALUE_TYPE_060921_HPP
   6 # define BOOST_PARAMETER_VALUE_TYPE_060921_HPP
   7
   8 # include <boost/mpl/apply.hpp>
   9 # include <boost/mpl/assert.hpp>
  10 # include <boost/mpl/and.hpp>
  11 # include <boost/parameter/aux_/result_of0.hpp>
  12 # include <boost/parameter/aux_/void.hpp>
  13 # include <boost/type_traits/is_same.hpp>
  14
  15 namespace boost { namespace parameter {
  16
  17 // A metafunction that, given an argument pack, returns the type of
  18 // the parameter identified by the given keyword.  If no such
  19 // parameter has been specified, returns Default
  20
  21 # if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
  22 template <class Parameters, class Keyword, class Default>
  23 struct value_type0
  24 {
  25     typedef typename mpl::apply_wrap3<
  26         typename Parameters::binding,Keyword,Default,mpl::false_
  27     >::type type;
  28
  29     BOOST_MPL_ASSERT_NOT((
  30         mpl::and_<
  31             is_same<Default, void_>
  32           , is_same<type, void_>
  33         >
  34     ));
  35 };
  36 # endif
  37
  38 template <class Parameters, class Keyword, class Default = void_>
  39 struct value_type
  40 {
  41 # if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
  42     typedef typename mpl::eval_if<
  43         mpl::is_placeholder<Parameters>
  44       , mpl::identity<int>
  45       , value_type0<Parameters,Keyword,Default>
  46     >::type type;
  47 # else
  48     typedef typename mpl::apply_wrap3<
  49         typename Parameters::binding,Keyword,Default,mpl::false_
  50     >::type type;
  51
  52     BOOST_MPL_ASSERT_NOT((
  53         mpl::and_<
  54             is_same<Default, void_>
  55           , is_same<type, void_>
  56         >
  57     ));
  58 # endif
  59
  60     BOOST_MPL_AUX_LAMBDA_SUPPORT(3,value_type,(Parameters,Keyword,Default))
  61 };
  62
  63 // A metafunction that, given an argument pack, returns the type of
  64 // the parameter identified by the given keyword.  If no such
  65 // parameter has been specified, returns the type returned by invoking
  66 // DefaultFn
  67 template <class Parameters, class Keyword, class DefaultFn>
  68 struct lazy_value_type
  69 {
  70   typedef typename mpl::apply_wrap3<
  71       typename Parameters::binding
  72     , Keyword
  73     , typename aux::result_of0<DefaultFn>::type
  74     , mpl::false_
  75   >::type type;
  76 };
  77
  78
  79 }} // namespace boost::parameter
  80
  81 #endif // BOOST_PARAMETER_VALUE_TYPE_060921_HPP
  82