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 #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 
70 namespace detail {
71 
72 template <typename T>
73 struct 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 
84 template< typename T > struct is_static_visitor
85 	: public ::boost::integral_constant<bool,(::boost::detail::is_static_visitor_impl<T>::value)>
86 {
87 public:
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