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7c673cae | 1 | // (C) Copyright Daniel Frey and Robert Ramey 2009. |
92f5a8d4 | 2 | // (C) Copyright Balint Cserni 2017 |
7c673cae FG |
3 | // Use, modification and distribution are subject to the Boost Software License, |
4 | // Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at | |
5 | // http://www.boost.org/LICENSE_1_0.txt). | |
6 | // | |
7 | // See http://www.boost.org/libs/type_traits for most recent version including documentation. | |
8 | ||
9 | #ifndef BOOST_TT_IS_VIRTUAL_BASE_OF_HPP_INCLUDED | |
10 | #define BOOST_TT_IS_VIRTUAL_BASE_OF_HPP_INCLUDED | |
11 | ||
12 | #include <boost/type_traits/is_base_of.hpp> | |
13 | #include <boost/type_traits/is_same.hpp> | |
92f5a8d4 TL |
14 | #include <boost/type_traits/make_void.hpp> |
15 | #include <utility> | |
7c673cae FG |
16 | |
17 | namespace boost { | |
92f5a8d4 | 18 | namespace detail { |
7c673cae FG |
19 | |
20 | ||
21 | #ifdef BOOST_MSVC | |
22 | #pragma warning( push ) | |
23 | #pragma warning( disable : 4584 4250 4594) | |
24 | #elif defined(__GNUC__) && (__GNUC__ >= 4) | |
25 | #pragma GCC system_header | |
26 | #endif | |
27 | ||
92f5a8d4 | 28 | #if !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) && !defined(BOOST_NO_CXX11_NULLPTR) && !BOOST_WORKAROUND(BOOST_GCC, < 40800) |
7c673cae | 29 | |
92f5a8d4 TL |
30 | // Implementation based on the standard's rules of explicit type conversions. |
31 | // A pointer to an object of *derived* class type may be explicitly converted to a pointer to an *unambiguous* *base* class type. | |
32 | // A pointer to an object of an *unambiguous* *non-virtual* *base* class type may be explicitly converted to a pointer of a *derived* class type. | |
33 | // Therefore Derived has a virtual base Base if and only if | |
34 | // (1) a Derived* can be converted to Base* (so the base class is unambiguous, which comes necessarily from virtual inheritance) | |
35 | // (2) a Base* cannot be converted to Derived* (so the base class is either ambiguous or virtual) | |
36 | // With both conditions true, Base must be a virtual base of Derived. | |
37 | // The "is_base_of" is only needed so the compiler can (but is not required to) error out if the types are incomplete. | |
38 | // This is in league with the the expected behaviour. | |
39 | ||
40 | template<class T, class U> | |
41 | constexpr bool is_virtual_base_impl(...) { return true; } | |
42 | ||
43 | // C-style casts have the power to ignore inheritance visibility while still act as a static_cast. | |
44 | // They can also fall back to the behaviour of reinterpret_cast, which allows is_virtual_base_of to work on non-class types too. | |
45 | // Note that because we are casting pointers there can be no user-defined operators to interfere. | |
46 | template<class T, class U, | |
47 | typename boost::make_void<decltype((U*)(std::declval<T*>()))>::type* = | |
48 | nullptr> | |
49 | constexpr bool is_virtual_base_impl(int) { return false; } | |
50 | ||
51 | } // namespace detail | |
52 | ||
53 | template<class T, class U> | |
54 | struct is_virtual_base_of : public | |
55 | boost::integral_constant< | |
56 | bool, | |
57 | boost::is_base_of<T, U>::value && | |
58 | detail::is_virtual_base_impl<T, U>(0) && | |
59 | !detail::is_virtual_base_impl<U, T>(0) | |
60 | > {}; | |
61 | ||
62 | #else | |
63 | ||
64 | template<typename Base, typename Derived, typename tag> | |
65 | struct is_virtual_base_of_impl | |
66 | { | |
67 | BOOST_STATIC_CONSTANT(bool, value = false); | |
68 | }; | |
69 | ||
70 | template<typename Base, typename Derived> | |
71 | struct is_virtual_base_of_impl<Base, Derived, true_type> | |
7c673cae | 72 | { |
92f5a8d4 TL |
73 | union max_align |
74 | { | |
75 | unsigned u; | |
76 | unsigned long ul; | |
77 | void* v; | |
78 | double d; | |
79 | long double ld; | |
7c673cae | 80 | #ifndef BOOST_NO_LONG_LONG |
92f5a8d4 | 81 | long long ll; |
7c673cae | 82 | #endif |
92f5a8d4 | 83 | }; |
20effc67 | 84 | #ifdef BOOST_BORLANDC |
92f5a8d4 TL |
85 | struct boost_type_traits_internal_struct_X : public virtual Derived, public virtual Base |
86 | { | |
87 | boost_type_traits_internal_struct_X(); | |
88 | boost_type_traits_internal_struct_X(const boost_type_traits_internal_struct_X&); | |
89 | boost_type_traits_internal_struct_X& operator=(const boost_type_traits_internal_struct_X&); | |
90 | ~boost_type_traits_internal_struct_X()throw(); | |
91 | max_align data[4]; | |
92 | }; | |
93 | struct boost_type_traits_internal_struct_Y : public virtual Derived | |
94 | { | |
95 | boost_type_traits_internal_struct_Y(); | |
96 | boost_type_traits_internal_struct_Y(const boost_type_traits_internal_struct_Y&); | |
97 | boost_type_traits_internal_struct_Y& operator=(const boost_type_traits_internal_struct_Y&); | |
98 | ~boost_type_traits_internal_struct_Y()throw(); | |
99 | max_align data[4]; | |
100 | }; | |
7c673cae | 101 | #else |
92f5a8d4 TL |
102 | struct boost_type_traits_internal_struct_X : public Derived, virtual Base |
103 | { | |
104 | boost_type_traits_internal_struct_X(); | |
105 | boost_type_traits_internal_struct_X(const boost_type_traits_internal_struct_X&); | |
106 | boost_type_traits_internal_struct_X& operator=(const boost_type_traits_internal_struct_X&); | |
107 | ~boost_type_traits_internal_struct_X()throw(); | |
108 | max_align data[16]; | |
109 | }; | |
110 | struct boost_type_traits_internal_struct_Y : public Derived | |
111 | { | |
112 | boost_type_traits_internal_struct_Y(); | |
113 | boost_type_traits_internal_struct_Y(const boost_type_traits_internal_struct_Y&); | |
114 | boost_type_traits_internal_struct_Y& operator=(const boost_type_traits_internal_struct_Y&); | |
115 | ~boost_type_traits_internal_struct_Y()throw(); | |
116 | max_align data[16]; | |
117 | }; | |
7c673cae | 118 | #endif |
92f5a8d4 TL |
119 | BOOST_STATIC_CONSTANT(bool, value = (sizeof(boost_type_traits_internal_struct_X) == sizeof(boost_type_traits_internal_struct_Y))); |
120 | }; | |
7c673cae | 121 | |
92f5a8d4 TL |
122 | template<typename Base, typename Derived> |
123 | struct is_virtual_base_of_impl2 | |
124 | { | |
125 | typedef boost::integral_constant<bool, (boost::is_base_of<Base, Derived>::value && !boost::is_same<Base, Derived>::value)> tag_type; | |
126 | typedef is_virtual_base_of_impl<Base, Derived, tag_type> imp; | |
127 | BOOST_STATIC_CONSTANT(bool, value = imp::value); | |
128 | }; | |
7c673cae FG |
129 | |
130 | } // namespace detail | |
131 | ||
92f5a8d4 TL |
132 | template <class Base, class Derived> struct is_virtual_base_of : public integral_constant<bool, (::boost::detail::is_virtual_base_of_impl2<Base, Derived>::value)> {}; |
133 | ||
134 | #endif | |
7c673cae FG |
135 | |
136 | template <class Base, class Derived> struct is_virtual_base_of<Base&, Derived> : public false_type{}; | |
137 | template <class Base, class Derived> struct is_virtual_base_of<Base, Derived&> : public false_type{}; | |
138 | template <class Base, class Derived> struct is_virtual_base_of<Base&, Derived&> : public false_type{}; | |
139 | ||
92f5a8d4 TL |
140 | #ifdef BOOST_MSVC |
141 | #pragma warning( pop ) | |
142 | #endif | |
143 | ||
7c673cae FG |
144 | } // namespace boost |
145 | ||
146 | #endif |