//-----------------------------------------------------------------------------

// boost variant/detail/visitation_impl.hpp header file

// See http://www.boost.org for updates, documentation, and revision history.

//-----------------------------------------------------------------------------

//

// Copyright (c) 2003

// Eric Friedman

//

// Distributed under 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_VARIANT_DETAIL_VISITATION_IMPL_HPP

#define BOOST_VARIANT_DETAIL_VISITATION_IMPL_HPP



#include "boost/config.hpp"



#include "boost/variant/detail/backup_holder.hpp"

#include "boost/variant/detail/cast_storage.hpp"

#include "boost/variant/detail/forced_return.hpp"

#include "boost/variant/detail/generic_result_type.hpp"



#include "boost/assert.hpp"

#include "boost/mpl/eval_if.hpp"

#include "boost/mpl/bool.hpp"

#include "boost/mpl/identity.hpp"

#include "boost/mpl/int.hpp"

#include "boost/mpl/next.hpp"

#include "boost/mpl/deref.hpp"

#include "boost/mpl/or.hpp"

#include "boost/preprocessor/cat.hpp"

#include "boost/preprocessor/inc.hpp"

#include "boost/preprocessor/repeat.hpp"

#include "boost/type_traits/is_same.hpp"

#include "boost/type_traits/has_nothrow_copy.hpp"

#include "boost/variant/detail/has_nothrow_move.hpp"





///////////////////////////////////////////////////////////////////////////////

// BOOST_VARIANT_VISITATION_UNROLLING_LIMIT

//

// Unrolls variant's visitation mechanism to reduce template instantiation

// and potentially increase runtime performance. (TODO: Investigate further.)

//

#if !defined(BOOST_VARIANT_VISITATION_UNROLLING_LIMIT)

#   define BOOST_VARIANT_VISITATION_UNROLLING_LIMIT   \

        BOOST_VARIANT_LIMIT_TYPES

#endif



namespace boost {

namespace detail { namespace variant {



///////////////////////////////////////////////////////////////////////////////

// (detail) class apply_visitor_unrolled

//

// Tag type indicates when visitation_impl is unrolled.

//

struct apply_visitor_unrolled {};



///////////////////////////////////////////////////////////////////////////////

// (detail) class template visitation_impl_step

//

// "Never ending" iterator range facilitates visitation_impl unrolling.

//



#if !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)



template <typename Iter, typename LastIter>

struct visitation_impl_step

{

    typedef typename mpl::deref<Iter>::type type;



    typedef typename mpl::next<Iter>::type next_iter;

    typedef visitation_impl_step<

          next_iter, LastIter

        > next;

};



template <typename LastIter>

struct visitation_impl_step< LastIter,LastIter >

{

    typedef apply_visitor_unrolled type;

    typedef visitation_impl_step next;

};



#else // defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)



template <typename Iter, typename LastIter>

struct visitation_impl_step

{

    typedef typename mpl::eval_if<

          is_same<Iter, LastIter>

        , mpl::identity<apply_visitor_unrolled>

        , Iter

        >::type type;



    typedef typename mpl::eval_if<

          is_same<type, apply_visitor_unrolled> //is_same<Iter, LastIter>

        , mpl::identity<LastIter>

        , mpl::next<Iter>

        >::type next_iter;



    typedef visitation_impl_step<

          next_iter, LastIter

        > next;

};



#endif // BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION workaround



///////////////////////////////////////////////////////////////////////////////

// (detail) function template visitation_impl_invoke

//

// Invokes the given visitor on the specified type in the given storage.

//



template <typename Visitor, typename VoidPtrCV, typename T>

inline

    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)

visitation_impl_invoke_impl(

      int, Visitor& visitor, VoidPtrCV storage, T*

    , mpl::true_// never_uses_backup

    )

{

    return visitor.internal_visit(

          cast_storage<T>(storage), 1L

        );

}



template <typename Visitor, typename VoidPtrCV, typename T>

inline

    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)

visitation_impl_invoke_impl(

      int internal_which, Visitor& visitor, VoidPtrCV storage, T*

    , mpl::false_// never_uses_backup

    )

{

    if (internal_which >= 0)

    {

        return visitor.internal_visit(

              cast_storage<T>(storage), 1L

            );

    }

    else

    {

        return visitor.internal_visit(

              cast_storage< backup_holder<T> >(storage), 1L

            );

    }

}



template <typename Visitor, typename VoidPtrCV, typename T, typename NoBackupFlag>

inline

    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)

visitation_impl_invoke(

      int internal_which, Visitor& visitor, VoidPtrCV storage, T* t

    , NoBackupFlag

    , int

    )

{

    typedef typename mpl::or_<

          NoBackupFlag

        , has_nothrow_move_constructor<T>

        , has_nothrow_copy<T>

        >::type never_uses_backup;



    return visitation_impl_invoke_impl(

          internal_which, visitor, storage, t

        , never_uses_backup()

        );

}



template <typename Visitor, typename VoidPtrCV, typename NBF>

inline

    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)

visitation_impl_invoke(int, Visitor&, VoidPtrCV, apply_visitor_unrolled*, NBF, long)

{

    // should never be here at runtime:

    BOOST_ASSERT(false);

    typedef typename Visitor::result_type result_type;

    return ::boost::detail::variant::forced_return< result_type >();

}



///////////////////////////////////////////////////////////////////////////////

// (detail) function template visitation_impl

//

// Invokes the given visitor on the type in the given variant storage.

//



template <

      typename W, typename S

    , typename Visitor, typename VPCV

    , typename NBF

    >

inline

    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)

visitation_impl(

      int, int, Visitor&, VPCV

    , mpl::true_ // is_apply_visitor_unrolled

    , NBF, W* = 0, S* = 0

    )

{

    // should never be here at runtime:

    BOOST_ASSERT(false);

    typedef typename Visitor::result_type result_type;

    return ::boost::detail::variant::forced_return< result_type >();

}



template <

      typename Which, typename step0

    , typename Visitor, typename VoidPtrCV

    , typename NoBackupFlag

    >

inline

    BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)

visitation_impl(

      const int internal_which, const int logical_which

    , Visitor& visitor, VoidPtrCV storage

    , mpl::false_ // is_apply_visitor_unrolled

    , NoBackupFlag no_backup_flag

    , Which* = 0, step0* = 0

    )

{

    // Typedef apply_visitor_unrolled steps and associated types...

#   define BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_TYPEDEF(z, N, _) \

    typedef typename BOOST_PP_CAT(step,N)::type BOOST_PP_CAT(T,N); \

    typedef typename BOOST_PP_CAT(step,N)::next \

        BOOST_PP_CAT(step, BOOST_PP_INC(N)); \

    /**/



    BOOST_PP_REPEAT(

          BOOST_VARIANT_VISITATION_UNROLLING_LIMIT

        , BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_TYPEDEF

        , _

        )



#   undef BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_TYPEDEF



    // ...switch on the target which-index value...

    switch (logical_which)

    {



    // ...applying the appropriate case:

#   define BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_CASE(z, N, _) \

    case (Which::value + (N)): \

        return visitation_impl_invoke( \

              internal_which, visitor, storage \

            , static_cast<BOOST_PP_CAT(T,N)*>(0) \

            , no_backup_flag, 1L \

            ); \

    /**/



    BOOST_PP_REPEAT(

          BOOST_VARIANT_VISITATION_UNROLLING_LIMIT

        , BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_CASE

        , _

        )



#   undef BOOST_VARIANT_AUX_APPLY_VISITOR_STEP_CASE



    }



    // If not handled in this iteration, continue unrolling:

    typedef mpl::int_<

          Which::value + (BOOST_VARIANT_VISITATION_UNROLLING_LIMIT)

        > next_which;



    typedef BOOST_PP_CAT(step, BOOST_VARIANT_VISITATION_UNROLLING_LIMIT)

        next_step;



    typedef typename next_step::type next_type;

    typedef typename is_same< next_type,apply_visitor_unrolled >::type

        is_apply_visitor_unrolled;



    return visitation_impl(

          internal_which, logical_which

        , visitor, storage

        , is_apply_visitor_unrolled()

        , no_backup_flag

        , static_cast<next_which*>(0), static_cast<next_step*>(0)

        );

}



}} // namespace detail::variant

} // namespace boost



#endif // BOOST_VARIANT_DETAIL_VISITATION_IMPL_HPP

