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 
25 namespace 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 
34 namespace detail {
35 
36     struct is_static_visitor_tag { };
37 
38     typedef void static_visitor_default_return;
39 
40 } // namespace detail
41 
42 template <typename R = ::boost::detail::static_visitor_default_return>
43 class static_visitor
44     : public detail::is_static_visitor_tag
45 {
46 public: // typedefs
47 
48     typedef R result_type;
49 
50 protected: // 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     ~static_visitor() = default;
54 #else
55     static_visitor()  BOOST_NOEXCEPT { }
56     ~static_visitor()  BOOST_NOEXCEPT { }
57 #endif
58 };
59 
60 //////////////////////////////////////////////////////////////////////////
61 // metafunction is_static_visitor
62 //
63 // Value metafunction indicates whether the specified type derives from
64 // static_visitor<...>.
65 //
66 // NOTE #1: This metafunction does NOT check whether the specified type
67 //  fulfills the requirements of the StaticVisitor concept.
68 //
69 // NOTE #2: This template never needs to be specialized!
70 //
71 
72 namespace detail {
73 
74 template <typename T>
75 struct is_static_visitor_impl
76 {
77     BOOST_STATIC_CONSTANT(bool, value =
78         (::boost::is_base_and_derived<
79             detail::is_static_visitor_tag,
80             T
81         >::value));
82 };
83 
84 } // namespace detail
85 
86 template< typename T > struct is_static_visitor
87 	: public ::boost::integral_constant<bool,(::boost::detail::is_static_visitor_impl<T>::value)>
88 {
89 public:
90     BOOST_MPL_AUX_LAMBDA_SUPPORT(1,is_static_visitor,(T))
91 };
92 
93 } // namespace boost
94 
95 #endif // BOOST_VARIANT_STATIC_VISITOR_HPP
96