ceph/src/boost/libs/function_types/example/detail/param_type.hpp

   1
   2 // (C) Copyright Tobias Schwinger
   3 //
   4 // Use modification and distribution are subject to the boost Software License,
   5 // Version 1.0. (See http://www.boost.org/LICENSE_1_0.txt).
   6
   7 //------------------------------------------------------------------------------
   8
   9 // Metafunction to compute optimal parameter type for argument forwarding.
  10
  11 // This header is not an FT example in itself -- it's used by some of them to
  12 // optimize argument forwarding.
  13 //
  14 // For more details see 'fast_mem_fn.hpp' in this directory or the documentation
  15 // of the CallTraits utility [1].
  16 //
  17 //
  18 // References
  19 // ==========
  20 //
  21 // [1] http://www.boost.org/libs/utility/call_traits.htm
  22
  23 #ifndef BOOST_UTILITY_PARAM_TYPE_HPP_INCLUDED
  24 #define BOOST_UTILITY_PARAM_TYPE_HPP_INCLUDED
  25
  26 #include <boost/config.hpp>
  27
  28 #include <boost/type_traits/add_const.hpp>
  29 #include <boost/type_traits/add_reference.hpp>
  30
  31 #include <boost/mpl/eval_if.hpp>
  32 #include <boost/mpl/identity.hpp>
  33
  34 #include <boost/mpl/aux_/lambda_support.hpp>
  35 // #include <boost/type_traits/detail/template_arity_spec.hpp>
  36
  37 // namespace boost
  38 namespace example
  39 {
  40   namespace mpl = boost::mpl;
  41
  42   // namespace utility
  43   // {
  44     namespace param_type_detail
  45     {
  46       template<typename T>
  47       struct by_ref_cond
  48       {
  49         typedef by_ref_cond type;
  50         BOOST_STATIC_CONSTANT(bool,value = sizeof(void*) < sizeof(T));
  51       };
  52
  53       template<typename T>
  54       struct add_ref_to_const
  55         : boost::add_reference< typename boost::add_const<T>::type >
  56       { };
  57     }
  58
  59     template<typename T>
  60     struct param_type
  61       : mpl::eval_if< param_type_detail::by_ref_cond<T>
  62                     , param_type_detail::add_ref_to_const<T>, mpl::identity<T> >
  63     {
  64       BOOST_MPL_AUX_LAMBDA_SUPPORT(1,param_type,(T))
  65     };
  66   // }
  67   // BOOST_TT_AUX_TEMPLATE_ARITY_SPEC(1,utility::param_type)
  68 }
  69
  70 #endif
  71