boost/variant/detail/forced_return.hpp
//-----------------------------------------------------------------------------
// boost variant/detail/forced_return.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_FORCED_RETURN_HPP
#define BOOST_VARIANT_DETAIL_FORCED_RETURN_HPP
#include "boost/config.hpp"
#include "boost/variant/detail/generic_result_type.hpp"
#include "boost/assert.hpp"
#if !defined(BOOST_MSVC) && !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION)
# include "boost/type_traits/remove_reference.hpp"
#endif
namespace boost {
namespace detail { namespace variant {
///////////////////////////////////////////////////////////////////////////////
// (detail) function template forced_return
//
// Logical error to permit invocation at runtime, but (artificially) satisfies
// compile-time requirement of returning a result value.
//
#if !defined(BOOST_MSVC) \
&& !defined(BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION) \
&& !defined(BOOST_NO_VOID_RETURNS)
// "standard" implementation:
template <typename T>
inline T forced_return( BOOST_EXPLICIT_TEMPLATE_TYPE(T) )
{
// logical error: should never be here! (see above)
BOOST_ASSERT(false);
typedef typename boost::remove_reference<T>::type basic_type;
basic_type* dummy = 0;
return *static_cast< basic_type* >(dummy);
}
template <>
inline void forced_return<void>( BOOST_EXPLICIT_TEMPLATE_TYPE_SPEC(void) )
{
// logical error: should never be here! (see above)
BOOST_ASSERT(false);
}
#elif !defined(BOOST_MSVC)
// workaround implementation
//
// TODO: Determine the most efficient way to handle this -- as below? by
// throwing? by recursive call to forced_return itself? etc.
//
template <typename T>
inline
BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(T)
forced_return( BOOST_EXPLICIT_TEMPLATE_TYPE(T) )
{
// logical error: should never be here! (see above)
BOOST_ASSERT(false);
BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(T) (*dummy)() = 0;
return dummy();
}
#else // defined(BOOST_MSVC)
// msvc-specific implementation
//
// Leverages __declspec(noreturn) for optimized implementation.
//
__declspec(noreturn)
inline void forced_return_no_return() {};
template <typename T>
inline
BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(T)
forced_return( BOOST_EXPLICIT_TEMPLATE_TYPE(T) )
{
// logical error: should never be here! (see above)
BOOST_ASSERT(false);
forced_return_no_return();
}
#endif // BOOST_MSVC optimization
}} // namespace detail::variant
} // namespace boost
#endif // BOOST_VARIANT_DETAIL_FORCED_RETURN_HPP