boost/flyweight/detail/not_placeholder_expr.hpp

   1 /* Copyright 2006-2008 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_NOT_PLACEHOLDER_EXPR_HPP
  10 #define BOOST_FLYWEIGHT_DETAIL_NOT_PLACEHOLDER_EXPR_HPP
  11
  12 #if defined(_MSC_VER)&&(_MSC_VER>=1200)
  13 #pragma once
  14 #endif
  15
  16 /* BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION can be inserted at the end
  17  * of a class template parameter declaration:
  18  *   template<
  19  *     typename X0,...,typename Xn
  20  *     BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION
  21  *   >
  22  *   struct foo...
  23  * to prevent instantiations from being treated as MPL placeholder
  24  * expressions in the presence of placeholder arguments; this is useful
  25  * to avoid masking of a metafunction class nested ::apply during
  26  * MPL invocation.
  27  */
  28
  29 #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
  30 #include <boost/detail/workaround.hpp>
  31
  32 #if BOOST_WORKAROUND(__GNUC__, <4)||\
  33     BOOST_WORKAROUND(__GNUC__,==4)&&(__GNUC_MINOR__<2)
  34 /* The default trick on which the macro is based, namely adding a int=0
  35  * defaulted template parameter, does not work in GCC prior to 4.2 due to
  36  * an unfortunate compiler non-standard extension, as explained in
  37  *   http://lists.boost.org/boost-users/2007/07/29866.php
  38  * We resort to an uglier technique, adding defaulted template parameters
  39  * so as to exceed BOOST_MPL_LIMIT_METAFUNCTION_ARITY.
  40  */
  41
  42 #include <boost/mpl/limits/arity.hpp>
  43 #include <boost/preprocessor/facilities/intercept.hpp>
  44 #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
  45
  46 #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION                  \
  47 BOOST_PP_ENUM_TRAILING_PARAMS(                                        \
  48   BOOST_MPL_LIMIT_METAFUNCTION_ARITY,typename=int BOOST_PP_INTERCEPT)
  49 #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION_DEF              \
  50 BOOST_PP_ENUM_TRAILING_PARAMS(                                        \
  51   BOOST_MPL_LIMIT_METAFUNCTION_ARITY,typename BOOST_PP_INTERCEPT)
  52
  53 #else
  54 #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION  ,int=0
  55 #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION_DEF  ,int
  56 #endif
  57
  58 #endif