boost/flyweight/detail/is_placeholder_expr.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_IS_PLACEHOLDER_EXPR_HPP
  10 #define BOOST_FLYWEIGHT_DETAIL_IS_PLACEHOLDER_EXPR_HPP
  11
  12 #if defined(_MSC_VER)
  13 #pragma once
  14 #endif
  15
  16 #include <boost/type_traits/is_same.hpp>
  17 #include <boost/mpl/apply.hpp>
  18 #include <boost/mpl/aux_/lambda_support.hpp>
  19 #include <boost/mpl/not.hpp>
  20 #include <boost/preprocessor/facilities/intercept.hpp>
  21 #include <boost/preprocessor/repetition/enum_params.hpp>
  22
  23 namespace boost{
  24
  25 namespace flyweights{
  26
  27 namespace detail{
  28
  29 /* is_placeholder_expression<T> indicates whether T is an
  30  * MPL placeholder expression.
  31  */
  32
  33 template<typename T>
  34 struct is_placeholder_expression_helper
  35 {
  36   template<
  37     BOOST_PP_ENUM_PARAMS(
  38       BOOST_MPL_LIMIT_METAFUNCTION_ARITY,typename BOOST_PP_INTERCEPT)
  39   >
  40   struct apply{
  41     typedef int type;
  42   };
  43
  44   BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_placeholder_expression_helper,(T))
  45 };
  46
  47 template<typename T>
  48 struct is_placeholder_expression:
  49   mpl::not_<is_same<
  50     typename mpl::apply<
  51       is_placeholder_expression_helper<T>,
  52       BOOST_PP_ENUM_PARAMS(
  53         BOOST_MPL_LIMIT_METAFUNCTION_ARITY,int BOOST_PP_INTERCEPT)
  54     >::type,
  55     int
  56   > >
  57 {};
  58
  59 } /* namespace flyweights::detail */
  60
  61 } /* namespace flyweights */
  62
  63 } /* namespace boost */
  64
  65 #endif