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boost/implicit_cast.hpp

// Copyright David Abrahams 2003. Permission to copy, use,
// modify, sell and distribute this software is granted provided this
// copyright notice appears in all copies. This software is provided
// "as is" without express or implied warranty, and with no claim as
// to its suitability for any purpose.
#ifndef IMPLICIT_CAST_DWA200356_HPP
# define IMPLICIT_CAST_DWA200356_HPP

# include <boost/mpl/identity.hpp>

namespace boost {

// implementation originally suggested by C. Green in
// http://lists.boost.org/MailArchives/boost/msg00886.php

// The use of identity creates a non-deduced form, so that the
// explicit template argument must be supplied
template <typename T>
inline T implicit_cast (typename mpl::identity<T>::type x) {
    return x;
}

// incomplete return type now is here
//template <typename T>
//void implicit_cast (...);

// Macro for when you need a constant expression (Gennaro Prota)
#define BOOST_IMPLICIT_CAST(dst_type, expr)           \
          ( sizeof( implicit_cast<dst_type>(expr) )   \
                     ,                                \
            static_cast<dst_type>(expr)               \
          )

} // namespace boost

#endif // IMPLICIT_CAST_DWA200356_HPP