Chris@16: /* Copyright 2006-2008 Joaquin M Lopez Munoz.
Chris@16:  * Distributed under the Boost Software License, Version 1.0.
Chris@16:  * (See accompanying file LICENSE_1_0.txt or copy at
Chris@16:  * http://www.boost.org/LICENSE_1_0.txt)
Chris@16:  *
Chris@16:  * See http://www.boost.org/libs/flyweight for library home page.
Chris@16:  */
Chris@16: 
Chris@16: #ifndef BOOST_FLYWEIGHT_DETAIL_NOT_PLACEHOLDER_EXPR_HPP
Chris@16: #define BOOST_FLYWEIGHT_DETAIL_NOT_PLACEHOLDER_EXPR_HPP
Chris@16: 
Chris@101: #if defined(_MSC_VER)
Chris@16: #pragma once
Chris@16: #endif
Chris@16: 
Chris@16: /* BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION can be inserted at the end
Chris@16:  * of a class template parameter declaration:
Chris@16:  *   template<
Chris@16:  *     typename X0,...,typename Xn
Chris@16:  *     BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION  
Chris@16:  *   >
Chris@16:  *   struct foo...
Chris@16:  * to prevent instantiations from being treated as MPL placeholder
Chris@16:  * expressions in the presence of placeholder arguments; this is useful
Chris@16:  * to avoid masking of a metafunction class nested ::apply during
Chris@16:  * MPL invocation.
Chris@16:  */
Chris@16: 
Chris@16: #include <boost/config.hpp> /* keep it first to prevent nasty warns in MSVC */
Chris@16: #include <boost/detail/workaround.hpp>
Chris@16: 
Chris@16: #if BOOST_WORKAROUND(__GNUC__, <4)||\
Chris@16:     BOOST_WORKAROUND(__GNUC__,==4)&&(__GNUC_MINOR__<2)
Chris@16: /* The default trick on which the macro is based, namely adding a int=0
Chris@16:  * defaulted template parameter, does not work in GCC prior to 4.2 due to
Chris@16:  * an unfortunate compiler non-standard extension, as explained in
Chris@16:  *   http://lists.boost.org/boost-users/2007/07/29866.php
Chris@16:  * We resort to an uglier technique, adding defaulted template parameters
Chris@16:  * so as to exceed BOOST_MPL_LIMIT_METAFUNCTION_ARITY.
Chris@16:  */
Chris@16: 
Chris@16: #include <boost/mpl/limits/arity.hpp>
Chris@16: #include <boost/preprocessor/facilities/intercept.hpp>
Chris@16: #include <boost/preprocessor/repetition/enum_trailing_params.hpp>
Chris@16: 
Chris@16: #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION                  \
Chris@16: BOOST_PP_ENUM_TRAILING_PARAMS(                                        \
Chris@16:   BOOST_MPL_LIMIT_METAFUNCTION_ARITY,typename=int BOOST_PP_INTERCEPT)
Chris@16: #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION_DEF              \
Chris@16: BOOST_PP_ENUM_TRAILING_PARAMS(                                        \
Chris@16:   BOOST_MPL_LIMIT_METAFUNCTION_ARITY,typename BOOST_PP_INTERCEPT)
Chris@16: 
Chris@16: #else
Chris@16: #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION  ,int=0
Chris@16: #define BOOST_FLYWEIGHT_NOT_A_PLACEHOLDER_EXPRESSION_DEF  ,int
Chris@16: #endif
Chris@16: 
Chris@16: #endif