1//-----------------------------------------------------------------------------
2// boost variant/static_visitor.hpp header file
3// See http://www.boost.org for updates, documentation, and revision history.
4//-----------------------------------------------------------------------------
5//
6// Copyright (c) 2002-2003
7// Eric Friedman
8//
9// Distributed under the Boost Software License, Version 1.0. (See
10// accompanying file LICENSE_1_0.txt or copy at
11// http://www.boost.org/LICENSE_1_0.txt)
12
13#ifndef BOOST_VARIANT_STATIC_VISITOR_HPP
14#define BOOST_VARIANT_STATIC_VISITOR_HPP
15
16#include <boost/config.hpp>
17#include <boost/detail/workaround.hpp>
18
19#include <boost/mpl/if.hpp>
20#include <boost/type_traits/is_base_and_derived.hpp>
21
22#include <boost/type_traits/integral_constant.hpp>
23#include <boost/mpl/aux_/lambda_support.hpp>
24
25namespace boost {
26
27//////////////////////////////////////////////////////////////////////////
28// class template static_visitor
29//
30// An empty base class that typedefs the return type of a deriving static
31// visitor. The class is analogous to std::unary_function in this role.
32//
33
34namespace detail {
35
36 struct is_static_visitor_tag { };
37
38 typedef void static_visitor_default_return;
39
40} // namespace detail
41
42template <typename R = ::boost::detail::static_visitor_default_return>
43class static_visitor
44 : public detail::is_static_visitor_tag
45{
46public: // typedefs
47
48 typedef R result_type;
49
50protected: // for use as base class only
51#if !defined(BOOST_NO_CXX11_DEFAULTED_FUNCTIONS) && !defined(BOOST_NO_CXX11_NON_PUBLIC_DEFAULTED_FUNCTIONS)
52 static_visitor() = default;
53#else
54 static_visitor() BOOST_NOEXCEPT { }
55#endif
56};
57
58//////////////////////////////////////////////////////////////////////////
59// metafunction is_static_visitor
60//
61// Value metafunction indicates whether the specified type derives from
62// static_visitor<...>.
63//
64// NOTE #1: This metafunction does NOT check whether the specified type
65// fulfills the requirements of the StaticVisitor concept.
66//
67// NOTE #2: This template never needs to be specialized!
68//
69
70namespace detail {
71
72template <typename T>
73struct is_static_visitor_impl
74{
75 BOOST_STATIC_CONSTANT(bool, value =
76 (::boost::is_base_and_derived<
77 detail::is_static_visitor_tag,
78 T
79 >::value));
80};
81
82} // namespace detail
83
84template< typename T > struct is_static_visitor
85 : public ::boost::integral_constant<bool,(::boost::detail::is_static_visitor_impl<T>::value)>
86{
87public:
88 BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_static_visitor,(T))
89};
90
91} // namespace boost
92
93#endif // BOOST_VARIANT_STATIC_VISITOR_HPP
94