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//-----------------------------------------------------------------------------
// boost variant/get.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_GET_HPP
#define BOOST_VARIANT_GET_HPP
#include <exception>
#include "boost/config.hpp"
#include "boost/detail/workaround.hpp"
#include "boost/utility/addressof.hpp"
#include "boost/variant/variant_fwd.hpp"
#include "boost/type_traits/add_reference.hpp"
#include "boost/type_traits/add_pointer.hpp"
#if BOOST_WORKAROUND(BOOST_MSVC, < 1300)
# include "boost/mpl/bool.hpp"
# include "boost/mpl/or.hpp"
# include "boost/type_traits/is_same.hpp"
#endif
namespace boost {
//////////////////////////////////////////////////////////////////////////
// class bad_get
//
// The exception thrown in the event of a failed get of a value.
//
class bad_get
: public std::exception
{
public: // std::exception implementation
virtual const char * what() const throw()
{
return "boost::bad_get: "
"failed value get using boost::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_visitor
//
// Generic static visitor that: if the value is of the specified type,
// returns a pointer to the value it visits; else a null pointer.
//
template <typename T>
struct get_visitor
{
private: // private typedefs
typedef typename add_pointer<T>::type pointer;
typedef typename add_reference<T>::type reference;
public: // visitor typedefs
typedef pointer result_type;
public: // visitor interfaces
#if !BOOST_WORKAROUND(BOOST_MSVC, < 1300)
pointer operator()(reference operand) const
{
return boost::addressof(operand);
}
template <typename U>
pointer operator()(const U&) const
{
return static_cast<pointer>(0);
}
#else // MSVC6
private: // helpers, for visitor interfaces (below)
pointer execute_impl(reference operand, mpl::true_) const
{
return boost::addressof(operand);
}
template <typename U>
pointer execute_impl(const U& operand, mpl::false_) const
{
return static_cast<pointer>(0);
}
public: // visitor interfaces
template <typename U>
pointer operator()(U& operand) const
{
// MSVC6 finds normal implementation (above) ambiguous,
// so we must explicitly disambiguate
typedef typename mpl::or_<
is_same<U, T>
, is_same<const U, T>
>::type U_is_T;
return execute_impl(operand, U_is_T());
}
#endif // MSVC6 workaround
};
}} // namespace detail::variant
#if !BOOST_WORKAROUND(__BORLANDC__, BOOST_TESTED_AT(0x0551))
# define BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(t) \
BOOST_APPEND_EXPLICIT_TEMPLATE_TYPE(t)
#else
# define BOOST_VARIANT_AUX_GET_EXPLICIT_TEMPLATE_TYPE(t) \
, t* = 0
#endif
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_pointer<U>::type
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;
if (!operand) return static_cast<U_ptr>(0);
detail::variant::get_visitor<U> v;
return operand->apply_visitor(v);
}
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_pointer<const U>::type
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;
if (!operand) return static_cast<U_ptr>(0);
detail::variant::get_visitor<const U> v;
return operand->apply_visitor(v);
}
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_reference<U>::type
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 = get<U>(&operand);
if (!result)
throw bad_get();
return *result;
}
template <typename U, BOOST_VARIANT_ENUM_PARAMS(typename T) >
inline
typename add_reference<const U>::type
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 = get<const U>(&operand);
if (!result)
throw bad_get();
return *result;
}
} // namespace boost
#endif // BOOST_VARIANT_GET_HPP
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