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//-----------------------------------------------------------------------------
// boost variant/polymorphic_get.hpp header file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 2013 Antony Polukhin
//
// 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_POLYMORPHIC_GET_HPP
#define BOOST_VARIANT_POLYMORPHIC_GET_HPP
#include <exception>
#include "boost/config.hpp"
#include "boost/detail/workaround.hpp"
#include "boost/throw_exception.hpp"
#include "boost/utility/addressof.hpp"
#include "boost/variant/variant_fwd.hpp"
#include "boost/variant/get.hpp"
#include "boost/type_traits/add_reference.hpp"
#include "boost/type_traits/add_pointer.hpp"
#include "boost/type_traits/is_base_of.hpp"
namespace boost {
//////////////////////////////////////////////////////////////////////////
// class bad_polymorphic_get
//
// The exception thrown in the event of a failed get of a value.
//
class BOOST_SYMBOL_VISIBLE bad_polymorphic_get
: public bad_get
{
public: // std::exception implementation
virtual const char * what() const BOOST_NOEXCEPT_OR_NOTHROW
{
return "boost::bad_polymorphic_get: "
"failed value get using boost::polymorphic_get";
}
};
//////////////////////////////////////////////////////////////////////////
// function template get<T>
//
// Retrieves content of given variant object if content is of type T.
// Otherwise: pointer ver. returns 0; reference ver. throws bad_get.
//
namespace detail { namespace variant {
// (detail) class template get_polymorphic_visitor
//
// Generic static visitor that: if the value is of the specified
// type or of a type derived from specified, returns a pointer
// to the value it visits; else a null pointer.
//
template <typename Base>
struct get_polymorphic_visitor
{
private: // private typedefs
typedef typename add_pointer<Base>::type pointer;
typedef typename add_reference<Base>::type reference;
pointer get(reference operand, boost::true_type) const BOOST_NOEXCEPT
{
return boost::addressof(operand);
}
template <class T>
pointer get(T&, boost::false_type) const BOOST_NOEXCEPT
{
return static_cast<pointer>(0);
}
public: // visitor interfaces
typedef pointer result_type;
template <typename U>
pointer operator()(U& operand) const BOOST_NOEXCEPT
{
typedef boost::integral_constant<
bool,
boost::is_base_of<Base, U>::value || boost::is_same<Base, U>::value
> tag_t;
return get(operand, tag_t());
}
};
}} // namespace detail::variant
#ifndef BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE
# if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x0551))
# define BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(t)
# else
# define BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(t) \
, t* = 0
# endif
#endif
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_pointer<U>::type
polymorphic_get(
boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >* operand
BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U)
) BOOST_NOEXCEPT
{
typedef typename add_pointer<U>::type U_ptr;
if (!operand) return static_cast<U_ptr>(0);
detail::variant::get_polymorphic_visitor<U> v;
return operand->apply_visitor(v);
}
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_pointer<const U>::type
polymorphic_get(
const boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >* operand
BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U)
) BOOST_NOEXCEPT
{
typedef typename add_pointer<const U>::type U_ptr;
if (!operand) return static_cast<U_ptr>(0);
detail::variant::get_polymorphic_visitor<const U> v;
return operand->apply_visitor(v);
}
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_reference<U>::type
polymorphic_get(
boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >& operand
BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U)
)
{
typedef typename add_pointer<U>::type U_ptr;
U_ptr result = polymorphic_get<U>(&operand);
if (!result)
boost::throw_exception(bad_polymorphic_get());
return *result;
}
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_reference<const U>::type
polymorphic_get(
const boost::variant< BOOST_VARIANT_ENUM_PARAMS(T) >& operand
BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(U)
)
{
typedef typename add_pointer<const U>::type U_ptr;
U_ptr result = polymorphic_get<const U>(&operand);
if (!result)
boost::throw_exception(bad_polymorphic_get());
return *result;
}
} // namespace boost
#endif // BOOST_VARIANT_POLYMORPHIC_GET_HPP
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