variant.hpp

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//-----------------------------------------------------------------------------
// boost variant/variant.hpp header file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 2002-2003
// Eric Friedman, Itay Maman
//
// 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_VARIANT_HPP
#define BOOST_VARIANT_VARIANT_HPP

#include <cstddef> // for std::size_t
#include <new> // for placement new
#include <typeinfo> // for typeid, std::type_info

#include "boost/variant/detail/config.hpp"
#include "boost/mpl/aux_/config/eti.hpp"
#include "boost/mpl/aux_/value_wknd.hpp"

#include "boost/variant/variant_fwd.hpp"
#include "boost/variant/detail/backup_holder.hpp"
#include "boost/variant/detail/enable_recursive_fwd.hpp"
#include "boost/variant/detail/forced_return.hpp"
#include "boost/variant/detail/initializer.hpp"
#include "boost/variant/detail/make_variant_list.hpp"
#include "boost/variant/detail/over_sequence.hpp"
#include "boost/variant/detail/visitation_impl.hpp"

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

#include "boost/detail/reference_content.hpp"
#include "boost/aligned_storage.hpp"
#include "boost/blank.hpp"
#include "boost/static_assert.hpp"
#include "boost/preprocessor/cat.hpp"
#include "boost/preprocessor/repeat.hpp"
#include "boost/type_traits/alignment_of.hpp"
#include "boost/type_traits/add_const.hpp"
#include "boost/type_traits/has_nothrow_constructor.hpp"
#include "boost/type_traits/has_nothrow_copy.hpp"
#include "boost/type_traits/is_const.hpp"
#include "boost/type_traits/is_same.hpp"
#include "boost/utility/enable_if.hpp"
#include "boost/variant/recursive_wrapper_fwd.hpp"
#include "boost/variant/static_visitor.hpp"

#include "boost/mpl/eval_if.hpp"
#include "boost/mpl/begin_end.hpp"
#include "boost/mpl/bool.hpp"
#include "boost/mpl/empty.hpp"
#include "boost/mpl/find_if.hpp"
#include "boost/mpl/front.hpp"
#include "boost/mpl/identity.hpp"
#include "boost/mpl/if.hpp"
#include "boost/mpl/int.hpp"
#include "boost/mpl/is_sequence.hpp"
#include "boost/mpl/iterator_range.hpp"
#include "boost/mpl/iter_fold_if.hpp"
#include "boost/mpl/logical.hpp"
#include "boost/mpl/max_element.hpp"
#include "boost/mpl/next.hpp"
#include "boost/mpl/deref.hpp"
#include "boost/mpl/pair.hpp"
#include "boost/mpl/protect.hpp"
#include "boost/mpl/push_front.hpp"
#include "boost/mpl/same_as.hpp"
#include "boost/mpl/size_t.hpp"
#include "boost/mpl/sizeof.hpp"
#include "boost/mpl/transform.hpp"
#include "boost/mpl/assert.hpp"

///////////////////////////////////////////////////////////////////////////////
// Implementation Macros:
//
// BOOST_VARIANT_VISITATION_UNROLLING_LIMIT
//   Defined in boost/variant/detail/visitation_impl.hpp.
//
// BOOST_VARIANT_MINIMIZE_SIZE
//   When #defined, implementation employs all known means to minimize the
//   size of variant obje   cts. However, often unsuccessful due to alignment
//   issues, and potentially harmful to runtime speed, so not enabled by
//   default. (TODO: Investigate further.)

#if defined(BOOST_VARIANT_MINIMIZE_SIZE)
#   include <climits> // for SCHAR_MAX
#   include "boost/mpl/eval_if.hpp"
#   include "boost/mpl/equal_to.hpp"
#   include "boost/mpl/identity.hpp"
#   include "boost/mpl/int.hpp"
#   include "boost/mpl/if.hpp"
#   include "boost/mpl/less.hpp"
#   include "boost/mpl/long.hpp"
#   include "boost/mpl/O1_size.hpp"
#endif


namespace boost {

namespace detail { namespace variant {

///////////////////////////////////////////////////////////////////////////////
// (detail) metafunction max_value
//
// Finds the maximum value of the unary metafunction F over Sequence.
//
template <typename Sequence, typename F>
struct max_value
{
private: // helpers, for metafunction result (below)

    typedef typename mpl::transform1<Sequence, F>::type transformed_;
    typedef typename mpl::max_element<transformed_
          
        >::type max_it;

public: // metafunction result

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

};

///////////////////////////////////////////////////////////////////////////////
// (detail) metafunction find_fallback_type
//
// Provides a fallback (i.e., nothrow default-constructible) type from the
// specified sequence, or no_fallback_type if not found.
//
// This implementation is designed to prefer boost::blank over other potential
// fallback types, regardless of its position in the specified sequence.
//

class no_fallback_type;

struct find_fallback_type_pred
{
    template <typename Iterator>
    struct apply
    {
    private:
        typedef typename mpl::deref<Iterator>::type t_;

    public:
        typedef mpl::not_< has_nothrow_constructor<t_> > type;
    };
};

template <typename Types>
struct find_fallback_type
{
private: // helpers, for metafunction result (below)

    typedef typename mpl::end<Types>::type end_it;

    // [Find the first suitable fallback type...]

    typedef typename mpl::iter_fold_if<
          Types
        , mpl::int_<0>, mpl::protect< mpl::next<> >
        , mpl::protect< find_fallback_type_pred >
        >::type first_result_;

    typedef typename first_result_::first first_result_index;
    typedef typename first_result_::second first_result_it;

    // [...now search the rest of the sequence for boost::blank...]

    typedef typename mpl::iter_fold_if<
          mpl::iterator_range< first_result_it,end_it >
        , first_result_index, mpl::protect< mpl::next<> >
        , mpl::protect< mpl::not_same_as<boost::blank> >
        >::type second_result_;

    typedef typename second_result_::second second_result_it;

public: // metafunction result

    // [...and return the results of the search:]
    typedef typename mpl::eval_if<
          is_same< second_result_it,end_it >
        , mpl::if_<
              is_same< first_result_it,end_it >
            , mpl::pair< no_fallback_type,no_fallback_type >
            , first_result_
            >
        , mpl::identity< second_result_ >
        >::type type;

};

#if defined(BOOST_MPL_CFG_MSVC_60_ETI_BUG)

template<>
struct find_fallback_type<int>
{
    typedef mpl::pair< no_fallback_type,no_fallback_type > type;
};

#endif // BOOST_MPL_CFG_MSVC_60_ETI_BUG workaround

///////////////////////////////////////////////////////////////////////////////
// (detail) metafunction make_storage
//
// Provides an aligned storage type capable of holding any of the types
// specified in the given type-sequence.
//

template <typename Types, typename NeverUsesBackupFlag>
struct make_storage
{
private: // helpers, for metafunction result (below)

    typedef typename mpl::eval_if<
          NeverUsesBackupFlag
        , mpl::identity< Types >
        , mpl::push_front<
              Types, backup_holder<void*>
            >
        >::type types;

    typedef typename max_value<
          types, mpl::sizeof_<mpl::_1>
        >::type max_size;

#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x0551))

    typedef typename max_value<
          types, alignment_of<mpl::_1>
        >::type max_alignment;

#else // borland

    // temporary workaround -- use maximal alignment
    typedef mpl::size_t< -1 > max_alignment;

#endif // borland workaround

public: // metafunction result

#if !BOOST_WORKAROUND(BOOST_MSVC, <= 1300)

    typedef ::boost::aligned_storage<
          BOOST_MPL_AUX_VALUE_WKND(max_size)::value
        , BOOST_MPL_AUX_VALUE_WKND(max_alignment)::value
        > type;

#else // MSVC7 and below

    BOOST_STATIC_CONSTANT(std::size_t, msvc_max_size_c = max_size::value);
    BOOST_STATIC_CONSTANT(std::size_t, msvc_max_alignment_c = max_alignment::value);

    typedef ::boost::aligned_storage<
          msvc_max_size_c
        , msvc_max_alignment_c
        > type;

#endif // MSVC workaround

};

#if defined(BOOST_MPL_CFG_MSVC_60_ETI_BUG)

template<>
struct make_storage<int,int>
{
    typedef int type;
};

#endif // BOOST_MPL_CFG_MSVC_60_ETI_BUG workaround

///////////////////////////////////////////////////////////////////////////////
// (detail) class destroyer
//
// Internal visitor that destroys the value it visits.
//
struct destroyer
    : public static_visitor<>
{
public: // visitor interfaces

    template <typename T>
        BOOST_VARIANT_AUX_RETURN_VOID_TYPE
    internal_visit(T& operand, int) const
    {
        operand.~T();

#if BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x0551))
        operand; // suppresses warnings
#endif

        BOOST_VARIANT_AUX_RETURN_VOID;
    }

};

///////////////////////////////////////////////////////////////////////////////
// (detail) class template known_get
//
// Visitor that returns a reference to content of the specified type.
//
// Precondition: visited variant MUST contain logical content of type T.
//
template <typename T>
class known_get
    : public static_visitor<T&>
{

#if !BOOST_WORKAROUND(BOOST_MSVC, <= 1200)

public: // visitor interface

    T& operator()(T& operand) const
    {
        return operand;
    }

    template <typename U>
    T& operator()(U&) const
    {
        // logical error to be here: see precondition above
        BOOST_ASSERT(false);
        return ::boost::detail::variant::forced_return< T& >();
    }

#else // MSVC6

private: // helpers, for visitor interface (below)

    T& execute(T& operand, mpl::true_) const
    {
        return operand;
    }

    template <typename U>
    T& execute(U& operand, mpl::false_) const
    {
        // logical error to be here: see precondition above
        BOOST_ASSERT(false);
        return ::boost::detail::variant::forced_return< T& >();
    }

public: // visitor interface

    template <typename U>
    T& operator()(U& operand) const
    {
        typedef typename is_same< U,T >::type
            U_is_T;

        return execute(operand, U_is_T());
    }

#endif // MSVC6 workaround

};

///////////////////////////////////////////////////////////////////////////////
// (detail) class copy_into
//
// Internal visitor that copies the value it visits into the given buffer.
//
class copy_into
    : public static_visitor<>
{
private: // representation

    void* storage_;

public: // structors

    explicit copy_into(void* storage)
        : storage_(storage)
    {
    }

public: // internal visitor interface

    template <typename T>
        BOOST_VARIANT_AUX_RETURN_VOID_TYPE
    internal_visit(boost::detail::variant::backup_holder<T>& operand, long) const
    {
        new(storage_) T( operand.get() );
        BOOST_VARIANT_AUX_RETURN_VOID;
    }

    template <typename T>
        BOOST_VARIANT_AUX_RETURN_VOID_TYPE
    internal_visit(const boost::detail::variant::backup_holder<T>& operand, long) const
    {
        new(storage_) T( operand.get() );
        BOOST_VARIANT_AUX_RETURN_VOID;
    }

    template <typename T>
        BOOST_VARIANT_AUX_RETURN_VOID_TYPE
    internal_visit(const T& operand, int) const
    {
        new(storage_) T(operand);
        BOOST_VARIANT_AUX_RETURN_VOID;
    }

};

///////////////////////////////////////////////////////////////////////////////
// (detail) class assign_storage
//
// Internal visitor that assigns the given storage (which must be a
// constructed value of the same type) to the value it visits.
//
struct assign_storage
    : public static_visitor<>
{
private: // representation

    const void* rhs_storage_;

public: // structors

    explicit assign_storage(const void* rhs_storage)
        : rhs_storage_(rhs_storage)
    {
    }

public: // internal visitor interfaces

    template <typename T>
        BOOST_VARIANT_AUX_RETURN_VOID_TYPE
    internal_visit(backup_holder<T>& lhs_content, long) const
    {
        lhs_content.get()
            = static_cast< const backup_holder<T>* >(rhs_storage_)->get();
        BOOST_VARIANT_AUX_RETURN_VOID;
    }

    template <typename T>
        BOOST_VARIANT_AUX_RETURN_VOID_TYPE
    internal_visit(const backup_holder<T>& lhs_content, long) const
    {
        lhs_content.get()
            = static_cast< const backup_holder<T>* >(rhs_storage_)->get();
        BOOST_VARIANT_AUX_RETURN_VOID;
    }

    template <typename T>
        BOOST_VARIANT_AUX_RETURN_VOID_TYPE
    internal_visit(T& lhs_content, int) const
    {
        // NOTE TO USER :
        // Compile error here indicates one of variant's bounded types does
        // not meet the requirements of the Assignable concept. Thus,
        // variant is not Assignable.
        //