boost/parameter/aux_/cast.hpp

// Copyright Daniel Wallin 2006. Use, modification and distribution is
// subject to the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_PARAMETER_CAST_060902_HPP
# define BOOST_PARAMETER_CAST_060902_HPP
# include <boost/detail/workaround.hpp>
# if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
#  include <boost/type_traits/add_reference.hpp>
#  include <boost/type_traits/remove_const.hpp>
# endif
namespace boost { namespace parameter { namespace aux {
struct use_default_tag {};
# if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x564))
#  define BOOST_PARAMETER_FUNCTION_CAST(value, predicate) value
# else
// Handles possible implicit casts. Used by preprocessor.hpp to
// normalize user input.
//
// cast<void*>::execute() is identity
// cast<void*(X)>::execute() is identity
// cast<void(X)>::execute() casts to X
//
// preprocessor.hpp uses this like this:
//
//   #define X(value, predicate)
//      cast<void predicate>::execute(value)
//
//   X(something, *)
//   X(something, *(predicate))
//   X(something, (int))
template <class T, class Args>
struct cast;
template <class Args>
struct cast<void*, Args>
{
    static use_default_tag execute(use_default_tag)
    {
        return use_default_tag();
    }
    static use_default_tag remove_const(use_default_tag)
    {
        return use_default_tag();
    }
    template <class U>
    static U& execute(U& value)
    {
        return value;
    }
    template <class U>
    static U& remove_const(U& x)
    {
        return x;
    }
};
#if BOOST_WORKAROUND(__SUNPRO_CC, BOOST_TESTED_AT(0x580))
typedef void* voidstar;
template <class T, class Args>
struct cast<voidstar(T), Args>
  : cast<void*, Args>
{
};
#else
template <class T, class Args>
struct cast<void*(T), Args>
  : cast<void*, Args>
{
};
#endif
// This is a hack used in cast<> to turn the user supplied type,
// which may or may not be a placeholder expression into one, so
// that it will be properly evaluated by mpl::apply.
template <class T, class Dummy = mpl::_1>
struct as_placeholder_expr
{
    typedef T type;
};
template <class T, class Args>
struct cast<void(T), Args>
{
    typedef typename mpl::apply2<
        as_placeholder_expr<T>, Args, Args>::type type0;
    typedef typename boost::add_reference<
        typename boost::remove_const<type0>::type 
    >::type reference;
    static use_default_tag execute(use_default_tag)
    {
        return use_default_tag();
    }
    static use_default_tag remove_const(use_default_tag)
    {
        return use_default_tag();
    }
    static type0 execute(type0 value)
    {
        return value;
    }
    template <class U>
    static reference remove_const(U const& x)
    {
        return const_cast<reference>(x);
    }
};
#  define BOOST_PARAMETER_FUNCTION_CAST(value, predicate, args) \
    boost::parameter::aux::cast<void predicate, args>::remove_const( \
        boost::parameter::aux::cast<void predicate, args>::execute(value) \
    )
# endif
}}} // namespace boost::parameter::aux
#endif // BOOST_PARAMETER_CAST_060902_HPP