boost/flyweight/detail/nested_xxx_if_not_ph.hpp

   1 /* Copyright 2006-2009 Joaquin M Lopez Munoz.
   2  * Distributed under the Boost Software License, Version 1.0.
   3  * (See accompanying file LICENSE_1_0.txt or copy at
   4  * http://www.boost.org/LICENSE_1_0.txt)
   5  *
   6  * See http://www.boost.org/libs/flyweight for library home page.
   7  */
   8
   9 #ifndef BOOST_FLYWEIGHT_DETAIL_NESTED_XXX_IF_NOT_PH_HPP
  10 #define BOOST_FLYWEIGHT_DETAIL_NESTED_XXX_IF_NOT_PH_HPP
  11
  12 #if defined(_MSC_VER)
  13 #pragma once
  14 #endif
  15
  16 #include <boost/flyweight/detail/is_placeholder_expr.hpp>
  17 #include <boost/mpl/if.hpp>
  18
  19 /* nested_##name##_if_not_placeholder_expression<T>::type is T::name unless
  20  * T is an MPL placeholder expression, in which case it defaults to int.
  21  */
  22
  23 #define BOOST_FLYWEIGHT_NESTED_XXX_IF_NOT_PLACEHOLDER_EXPRESSION_DEF(name) \
  24 struct nested_##name##_if_not_placeholder_expression_helper                \
  25 {                                                                          \
  26   typedef int name;                                                        \
  27 };                                                                         \
  28                                                                            \
  29 template<typename T>                                                       \
  30 struct nested_##name##_if_not_placeholder_expression                       \
  31 {                                                                          \
  32   typedef typename boost::mpl::if_<                                        \
  33     boost::flyweights::detail::is_placeholder_expression<T>,               \
  34     nested_##name##_if_not_placeholder_expression_helper,                  \
  35     T                                                                      \
  36   >::type::name type;                                                      \
  37 };
  38
  39 #endif