// (C) Copyright Jonathan Turkanis 2004.
// 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.

//
// Intended as an alternative to type_traits::yes_type and type_traits::no_type.
// Provides an arbitrary number of types (case_<0>, case_<1>, ...) for
// determining the results of overload resultion using 'sizeof', plus a uniform
// means of using the result. yes_type and no_type are typedefs for case_<1>
// and case_<0>. A single case with negative argument, case_<-1>, is also 
// provided, for convenience.
//
// This header may be included any number of times, with
// BOOST_SELECT_BY_SIZE_MAX_CASE defined to be the largest N such that case_<N>
// is needed for a particular application. It defaults to 2.
//
// This header depends only on Boost.Config and Boost.Preprocessor. Dependence
// on Type Traits or MPL was intentionally avoided, to leave open the 
// possibility that select_by_size could be used by these libraries.
//
// Example usage:
//
//    #define BOOST_SELECT_BY_SIZE_MAX_CASE 7         // Needed for > 2 cases.
//    #include <boost/utility/select_by_size.hpp>
//
//    using namespace boost::utility;
//
//    case_<0> helper(bool);           // could use 'case_<false>' or 'no_type'.
//    case_<1> helper(int);            // could use 'case_<true>' or' yes_type'.
//    case_<2> helper(unsigned);
//    case_<3> helper(long);
//    case_<4> helper(unsigned long);
//    case_<5> helper(float);
//    case_<6> helper(double);
//    case_<7> helper(const char*);
//
//    struct test {
//        static const int value =
//            select_by_size< sizeof(helper(9876UL)) >::value;
//        BOOST_STATIC_ASSERT(value == 4);
//    };
//
// For compilers with integral constant expression problems, e.g. Borland 5.x,
// one can also write
//
//    struct test {
//        BOOST_SELECT_BY_SIZE(int, value, helper(9876UL));
//    };
//
// to define a static integral constant 'value' equal to
//
//    select_by_size< sizeof(helper(9876UL)) >::value.
//

// Include guards surround all contents of this header except for explicit
// specializations of select_by_size for case_<N> with N > 2.

#ifndef BOOST_UTILITY_SELECT_BY_SIZE_HPP_INCLUDED
#define BOOST_UTILITY_SELECT_BY_SIZE_HPP_INCLUDED

// The lowest N for which select_by_size< sizeof(case_<N>) > has not been
// specialized.
#define SELECT_BY_SIZE_MAX_SPECIALIZED 2

#include <boost/config.hpp>    // BOOST_STATIC_CONSTANT.
#include <boost/preprocessor/arithmetic/inc.hpp>
#include <boost/preprocessor/cat.hpp>
#include <boost/preprocessor/repetition/repeat_from_to.hpp>
#include <boost/preprocessor/repetition/repeat_from_to.hpp>

/* Alternative implementation using max_align. 

#include <boost/type_traits/alignment_of.hpp>
#include <boost/type_traits/type_with_alignment.hpp>

namespace boost { namespace utility {

template<int N>
struct case_ { char c[(N + 1) * alignment_of<detail::max_align>::value]; };

template<unsigned Size>
struct select_by_size {
    BOOST_STATIC_CONSTANT(int, value = 
        (Size / alignment_of<detail::max_align>::value - 1));
};

} }             // End namespaces utility, boost.

*/              // End alternate implementation.

namespace boost { namespace utility {

//--------------Definition of case_-------------------------------------------//

template<int N> struct case_ { char c1; case_<N - 1> c2; };
template<> struct case_<-1> { char c; };
typedef case_<true> yes_type;
typedef case_<false> no_type;

//--------------Declaration of select_by_size---------------------------------//

template<unsigned Size> struct select_by_size;

} }             // End namespaces utility, boost.

//--------------Definition of SELECT_BY_SIZE_SPEC-----------------------------//

// Sepecializes select_by_size for sizeof(case<n-1>). The decrement is used
// here because the preprocessor library doesn't handle negative integers.
#define SELECT_BY_SIZE_SPEC(n)                                                 \
    namespace boost { namespace utility {                                      \
      namespace detail {                                                       \
        static const int BOOST_PP_CAT(sizeof_case_, n) = sizeof(case_<n - 1>); \
      }                                                                        \
      template<>                                                               \
      struct select_by_size< detail::BOOST_PP_CAT(sizeof_case_, n) > {         \
          struct type { BOOST_STATIC_CONSTANT(int, value = n - 1); };          \
          BOOST_STATIC_CONSTANT(int, value = type::value);                     \
      };                                                                       \
    } }                                                                        \
    /**/

//--------------Default specializations of select_by_size---------------------//

SELECT_BY_SIZE_SPEC(0) // select_by_size< sizeof(case<-1>) >
SELECT_BY_SIZE_SPEC(1) // select_by_size< sizeof(case<0>) >
SELECT_BY_SIZE_SPEC(2) // select_by_size< sizeof(case<1>) >

//--------------Definition of SELECT_BY_SIZE----------------------------------//

#define BOOST_SELECT_BY_SIZE(type_, name, expr)                                \
    BOOST_STATIC_CONSTANT(                                                     \
        unsigned,                                                              \
        BOOST_PP_CAT(boost_select_by_size_temp_, name) = sizeof(expr)          \
    );                                                                         \
    BOOST_STATIC_CONSTANT(                                                     \
        type_,                                                                 \
        name =                                                                 \
            ( boost::utility::select_by_size<                                  \
                BOOST_PP_CAT(boost_select_by_size_temp_, name)                 \
              >::value )                                                       \
    )                                                                          \
    /**/

#endif          // #ifndef BOOST_UTILITY_SELECT_BY_SIZE_HPP_INCLUDED

//----------Specializations of SELECT_BY_SIZE (outside main inclued guards)---//

// Specialize select_by_size for sizeof(case_<N>) for each N less than
// BOOST_SELECT_BY_SIZE_CASES for which this specialization has not already been
// performed.

#if !BOOST_PP_IS_ITERATING //-------------------------------------------------//
    #include <boost/preprocessor/iteration/iterate.hpp>
    #if !defined(BOOST_SELECT_BY_SIZE_MAX_CASE) || \
        (BOOST_SELECT_BY_SIZE_MAX_CASE < 2)
        #undef BOOST_SELECT_BY_SIZE_MAX_CASE
        #define BOOST_SELECT_BY_SIZE_MAX_CASE 2
    #endif

    #if (BOOST_SELECT_BY_SIZE_MAX_CASE > SELECT_BY_SIZE_MAX_SPECIALIZED)
        #define BOOST_PP_FILENAME_1 <boost/utility/select_by_size.hpp>
        #define BOOST_PP_ITERATION_LIMITS ( SELECT_BY_SIZE_MAX_SPECIALIZED, \
                                            BOOST_SELECT_BY_SIZE_MAX_CASE )
        #include BOOST_PP_ITERATE()
        #undef SELECT_BY_SIZE_MAX_SPECIALIZED
        #define SELECT_BY_SIZE_MAX_SPECIALIZED BOOST_SELECT_BY_SIZE_MAX_CASE
    #endif // #if (BOOST_SELECT_BY_SIZE_CASES > SELECT_BY_SIZE_MAX_SPECIALIZED)

    #undef BOOST_SELECT_BY_SIZE_MAX_CASE
#else // #if !BOOST_PP_IS_ITERATING //----------------------------------------//
    SELECT_BY_SIZE_SPEC(BOOST_PP_INC(BOOST_PP_ITERATION()))
#endif // #if !BOOST_PP_IS_ITERATING //---------------------------------------//