ext-boost/boost/variant/detail/apply_visitor_unary.hpp
2017-03-12 21:30:15 -07:00

174 lines
5.5 KiB
C++

//-----------------------------------------------------------------------------
// boost variant/detail/apply_visitor_unary.hpp header file
// See http://www.boost.org for updates, documentation, and revision history.
//-----------------------------------------------------------------------------
//
// Copyright (c) 2002-2003 Eric Friedman
// Copyright (c) 2014 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_DETAIL_APPLY_VISITOR_UNARY_HPP
#define BOOST_VARIANT_DETAIL_APPLY_VISITOR_UNARY_HPP
#include <boost/config.hpp>
#include <boost/detail/workaround.hpp>
#include <boost/variant/detail/generic_result_type.hpp>
#if BOOST_WORKAROUND(__EDG__, BOOST_TESTED_AT(302))
#include <boost/core/enable_if.hpp>
#include <boost/mpl/not.hpp>
#include <boost/type_traits/is_const.hpp>
#endif
#if !defined(BOOST_NO_CXX14_DECLTYPE_AUTO) && !defined(BOOST_NO_CXX11_DECLTYPE_N3276)
# include <boost/mpl/distance.hpp>
# include <boost/mpl/advance.hpp>
# include <boost/mpl/deref.hpp>
# include <boost/mpl/size.hpp>
# include <boost/utility/declval.hpp>
# include <boost/core/enable_if.hpp>
# include <boost/variant/detail/has_result_type.hpp>
#endif
namespace boost {
//////////////////////////////////////////////////////////////////////////
// function template apply_visitor(visitor, visitable)
//
// Visits visitable with visitor.
//
//
// nonconst-visitor version:
//
#if !BOOST_WORKAROUND(__EDG__, BOOST_TESTED_AT(302))
# define BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE(V) \
BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename V::result_type) \
/**/
#else // EDG-based compilers
# define BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE(V) \
typename enable_if< \
mpl::not_< is_const< V > > \
, BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename V::result_type) \
>::type \
/**/
#endif // EDG-based compilers workaround
template <typename Visitor, typename Visitable>
inline
BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE(Visitor)
apply_visitor(Visitor& visitor, Visitable& visitable)
{
return visitable.apply_visitor(visitor);
}
#undef BOOST_VARIANT_AUX_APPLY_VISITOR_NON_CONST_RESULT_TYPE
//
// const-visitor version:
//
template <typename Visitor, typename Visitable>
inline
BOOST_VARIANT_AUX_GENERIC_RESULT_TYPE(typename Visitor::result_type)
apply_visitor(const Visitor& visitor, Visitable& visitable)
{
return visitable.apply_visitor(visitor);
}
#if !defined(BOOST_NO_CXX14_DECLTYPE_AUTO) && !defined(BOOST_NO_CXX11_DECLTYPE_N3276)
// C++14
namespace detail { namespace variant {
// This class serves only metaprogramming purposes. none of its methods must be called at runtime!
template <class Visitor, class Variant>
struct result_multideduce1 {
typedef typename Variant::types types;
typedef typename boost::mpl::begin<types>::type begin_it;
typedef typename boost::mpl::advance<
begin_it, boost::mpl::int_<boost::mpl::size<types>::type::value - 1>
>::type last_it;
// For metaprogramming purposes ONLY! Do not use this method (and class) at runtime!
static Visitor& vis() BOOST_NOEXCEPT {
// Functions that work with lambdas must be defined in same translation unit.
// Because of that, we can not use `boost::decval<Visitor&>()` here.
Visitor&(*f)() = 0; // pointer to function
return f();
}
static decltype(auto) deduce_impl(last_it, unsigned /*helper*/) {
typedef typename boost::mpl::deref<last_it>::type value_t;
return vis()( boost::declval< value_t& >() );
}
template <class It>
static decltype(auto) deduce_impl(It, unsigned helper) {
typedef typename boost::mpl::next<It>::type next_t;
typedef typename boost::mpl::deref<It>::type value_t;
if (helper == boost::mpl::distance<begin_it, It>::type::value) {
return deduce_impl(next_t(), ++helper);
}
return vis()( boost::declval< value_t& >() );
}
static decltype(auto) deduce() {
return deduce_impl(begin_it(), 0);
}
};
template <class Visitor, class Variant>
struct result_wrapper1
{
typedef decltype(result_multideduce1<Visitor, Variant>::deduce()) result_type;
Visitor& visitor_;
explicit result_wrapper1(Visitor& visitor) BOOST_NOEXCEPT
: visitor_(visitor)
{}
template <class T>
result_type operator()(T& val) const {
return visitor_(val);
}
};
}} // namespace detail::variant
template <typename Visitor, typename Visitable>
inline decltype(auto) apply_visitor(Visitor& visitor, Visitable& visitable,
typename boost::disable_if<
boost::detail::variant::has_result_type<Visitor>
>::type* = 0)
{
boost::detail::variant::result_wrapper1<Visitor, Visitable> cpp14_vis(visitor);
return visitable.apply_visitor(cpp14_vis);
}
template <typename Visitor, typename Visitable>
inline decltype(auto) apply_visitor(const Visitor& visitor, Visitable& visitable,
typename boost::disable_if<
boost::detail::variant::has_result_type<Visitor>
>::type* = 0)
{
boost::detail::variant::result_wrapper1<const Visitor, Visitable> cpp14_vis(visitor);
return visitable.apply_visitor(cpp14_vis);
}
#endif // !defined(BOOST_NO_CXX14_DECLTYPE_AUTO) && !defined(BOOST_NO_CXX11_DECLTYPE_N3276)
} // namespace boost
#endif // BOOST_VARIANT_DETAIL_APPLY_VISITOR_UNARY_HPP