boost/variant/variant_fwd.hpp
//-----------------------------------------------------------------------------
// boost variant/variant_fwd.hpp header file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 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_FWD_HPP
#define BOOST_VARIANT_VARIANT_FWD_HPP
#include "boost/variant/detail/config.hpp"
#include "boost/blank_fwd.hpp"
#include "boost/mpl/arg.hpp"
#include "boost/mpl/limits/arity.hpp"
#include "boost/mpl/aux_/na.hpp"
#include "boost/preprocessor/cat.hpp"
#include "boost/preprocessor/enum.hpp"
#include "boost/preprocessor/enum_params.hpp"
#include "boost/preprocessor/enum_shifted_params.hpp"
#include "boost/preprocessor/repeat.hpp"
///////////////////////////////////////////////////////////////////////////////
// macro BOOST_VARIANT_LIMIT_TYPES
//
// Implementation-defined preprocessor symbol describing the actual
// length of variant's pseudo-variadic template parameter list.
//
#include "boost/mpl/limits/list.hpp"
#define BOOST_VARIANT_LIMIT_TYPES \
BOOST_MPL_LIMIT_LIST_SIZE
///////////////////////////////////////////////////////////////////////////////
// macro BOOST_VARIANT_NO_REFERENCE_SUPPORT
//
// Defined if variant does not support references as bounded types.
//
#if defined(BOOST_VARIANT_AUX_BROKEN_CONSTRUCTOR_TEMPLATE_ORDERING) \
&& !defined(BOOST_VARIANT_AUX_HAS_CONSTRUCTOR_TEMPLATE_ORDERING_SFINAE_WKND) \
&& !defined(BOOST_VARIANT_NO_REFERENCE_SUPPORT)
# define BOOST_VARIANT_NO_REFERENCE_SUPPORT
#endif
///////////////////////////////////////////////////////////////////////////////
// macro BOOST_VARIANT_NO_TYPE_SEQUENCE_SUPPORT
//
// Defined if variant does not support make_variant_over (see below).
//
#if defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
# define BOOST_VARIANT_NO_TYPE_SEQUENCE_SUPPORT
#endif
///////////////////////////////////////////////////////////////////////////////
// macro BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT
//
// Defined if make_recursive_variant cannot be supported as documented.
//
// Note: Currently, MPL lambda facility is used as workaround if defined, and
// so only types declared w/ MPL lambda workarounds will work.
//
#include "boost/variant/detail/substitute_fwd.hpp"
#if defined(BOOST_VARIANT_DETAIL_NO_SUBSTITUTE) \
&& !defined(BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT)
# define BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT
#endif
///////////////////////////////////////////////////////////////////////////////
// macro BOOST_VARIANT_RECURSIVE_VARIANT_MAX_ARITY
//
// Exposes maximum allowed arity of class templates with recursive_variant
// arguments. That is,
// make_recursive_variant< ..., T<[1], recursive_variant_, ... [N]> >.
//
#include "boost/mpl/limits/arity.hpp"
#define BOOST_VARIANT_RECURSIVE_VARIANT_MAX_ARITY \
BOOST_MPL_LIMIT_METAFUNCTION_ARITY
///////////////////////////////////////////////////////////////////////////////
// macro BOOST_VARIANT_ENUM_PARAMS
//
// Convenience macro for enumeration of BOOST_VARIANT_LIMIT_TYPES params.
//
// Rationale: Cleaner, simpler code for clients of variant library.
//
#define BOOST_VARIANT_ENUM_PARAMS( param ) \
BOOST_PP_ENUM_PARAMS(BOOST_VARIANT_LIMIT_TYPES, param)
///////////////////////////////////////////////////////////////////////////////
// macro BOOST_VARIANT_ENUM_SHIFTED_PARAMS
//
// Convenience macro for enumeration of BOOST_VARIANT_LIMIT_TYPES-1 params.
//
#define BOOST_VARIANT_ENUM_SHIFTED_PARAMS( param ) \
BOOST_PP_ENUM_SHIFTED_PARAMS(BOOST_VARIANT_LIMIT_TYPES, param)
namespace boost {
namespace detail { namespace variant {
///////////////////////////////////////////////////////////////////////////////
// (detail) class void_ and class template convert_void
//
// Provides the mechanism by which void(NN) types are converted to
// mpl::void_ (and thus can be passed to mpl::list).
//
// Rationale: This is particularly needed for the using-declarations
// workaround (below), but also to avoid associating mpl namespace with
// variant in argument dependent lookups (which used to happen because of
// defaulting of template parameters to mpl::void_).
//
struct void_;
template <typename T>
struct convert_void
{
typedef T type;
};
template <>
struct convert_void< void_ >
{
typedef mpl::na type;
};
///////////////////////////////////////////////////////////////////////////////
// (workaround) BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE
//
// Needed to work around compilers that don't support using-declaration
// overloads. (See the variant::initializer workarounds below.)
//
#if defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
// (detail) tags voidNN -- NN defined on [0, BOOST_VARIANT_LIMIT_TYPES)
//
// Defines void types that are each unique and specializations of
// convert_void that yields mpl::na for each voidNN type.
//
#define BOOST_VARIANT_DETAIL_DEFINE_VOID_N(z,N,_) \
struct BOOST_PP_CAT(void,N); \
\
template <> \
struct convert_void< BOOST_PP_CAT(void,N) > \
{ \
typedef mpl::na type; \
}; \
/**/
BOOST_PP_REPEAT(
BOOST_VARIANT_LIMIT_TYPES
, BOOST_VARIANT_DETAIL_DEFINE_VOID_N
, _
)
#undef BOOST_VARIANT_DETAIL_DEFINE_VOID_N
#endif // BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE workaround
}} // namespace detail::variant
///////////////////////////////////////////////////////////////////////////////
// (detail) macro BOOST_VARIANT_AUX_DECLARE_PARAM
//
// Template parameter list for variant and recursive_variant declarations.
//
#if !defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
# define BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL(z, N, T) \
typename BOOST_PP_CAT(T,N) = detail::variant::void_ \
/**/
#else // defined(BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE)
# define BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL(z, N, T) \
typename BOOST_PP_CAT(T,N) = BOOST_PP_CAT(detail::variant::void,N) \
/**/
#endif // BOOST_NO_USING_DECLARATION_OVERLOADS_FROM_TYPENAME_BASE workaround
#define BOOST_VARIANT_AUX_DECLARE_PARAMS \
BOOST_PP_ENUM( \
BOOST_VARIANT_LIMIT_TYPES \
, BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL \
, T \
) \
/**/
///////////////////////////////////////////////////////////////////////////////
// class template variant (concept inspired by Andrei Alexandrescu)
//
// Efficient, type-safe bounded discriminated union.
//
// Preconditions:
// - Each type must be unique.
// - No type may be const-qualified.
//
// Proper declaration form:
// variant<types> (where types is a type-sequence)
// or
// variant<T0,T1,...,Tn> (where T0 is NOT a type-sequence)
//
template < BOOST_VARIANT_AUX_DECLARE_PARAMS > class variant;
///////////////////////////////////////////////////////////////////////////////
// metafunction make_recursive_variant
//
// Exposes a boost::variant with recursive_variant_ tags (below) substituted
// with the variant itself (wrapped as needed with boost::recursive_wrapper).
//
template < BOOST_VARIANT_AUX_DECLARE_PARAMS > struct make_recursive_variant;
#undef BOOST_VARIANT_AUX_DECLARE_PARAMS_IMPL
#undef BOOST_VARIANT_AUX_DECLARE_PARAMS
///////////////////////////////////////////////////////////////////////////////
// type recursive_variant_
//
// Tag type indicates where recursive variant substitution should occur.
//
#if !defined(BOOST_VARIANT_NO_FULL_RECURSIVE_VARIANT_SUPPORT)
struct recursive_variant_ {};
#else
typedef mpl::arg<1> recursive_variant_;
#endif
///////////////////////////////////////////////////////////////////////////////
// metafunction make_variant_over
//
// Result is a variant w/ types of the specified type sequence.
//
template <typename Types> struct make_variant_over;
///////////////////////////////////////////////////////////////////////////////
// metafunction make_recursive_variant_over
//
// Result is a recursive variant w/ types of the specified type sequence.
//
template <typename Types> struct make_recursive_variant_over;
} // namespace boost
#endif // BOOST_VARIANT_VARIANT_FWD_HPP