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- // (C) Copyright Daniel Frey and Robert Ramey 2009.
- // (C) Copyright Balint Cserni 2017
- // Use, modification and distribution are subject to 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).
- //
- // See http://www.boost.org/libs/type_traits for most recent version including documentation.
-
- #ifndef BOOST_TT_IS_VIRTUAL_BASE_OF_HPP_INCLUDED
- #define BOOST_TT_IS_VIRTUAL_BASE_OF_HPP_INCLUDED
- #include <boost/type_traits/is_base_of.hpp>
- #include <boost/type_traits/is_same.hpp>
- #include <boost/type_traits/make_void.hpp>
- #include <utility>
- namespace boost {
- namespace detail {
- #ifdef BOOST_MSVC
- #pragma warning( push )
- #pragma warning( disable : 4584 4250 4594)
- #elif defined(__GNUC__) && (__GNUC__ >= 4)
- #pragma GCC system_header
- #endif
- #if !defined(BOOST_NO_SFINAE_EXPR) && !defined(BOOST_NO_CXX11_FUNCTION_TEMPLATE_DEFAULT_ARGS) && !defined(BOOST_NO_CXX11_NULLPTR) && !BOOST_WORKAROUND(BOOST_GCC, < 40800)
- // Implementation based on the standard's rules of explicit type conversions.
- // A pointer to an object of *derived* class type may be explicitly converted to a pointer to an *unambiguous* *base* class type.
- // 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.
- // Therefore Derived has a virtual base Base if and only if
- // (1) a Derived* can be converted to Base* (so the base class is unambiguous, which comes necessarily from virtual inheritance)
- // (2) a Base* cannot be converted to Derived* (so the base class is either ambiguous or virtual)
- // With both conditions true, Base must be a virtual base of Derived.
- // The "is_base_of" is only needed so the compiler can (but is not required to) error out if the types are incomplete.
- // This is in league with the the expected behaviour.
- template<class T, class U>
- constexpr bool is_virtual_base_impl(...) { return true; }
- // C-style casts have the power to ignore inheritance visibility while still act as a static_cast.
- // They can also fall back to the behaviour of reinterpret_cast, which allows is_virtual_base_of to work on non-class types too.
- // Note that because we are casting pointers there can be no user-defined operators to interfere.
- template<class T, class U,
- typename boost::make_void<decltype((U*)(std::declval<T*>()))>::type* =
- nullptr>
- constexpr bool is_virtual_base_impl(int) { return false; }
- } // namespace detail
- template<class T, class U>
- struct is_virtual_base_of : public
- boost::integral_constant<
- bool,
- boost::is_base_of<T, U>::value &&
- detail::is_virtual_base_impl<T, U>(0) &&
- !detail::is_virtual_base_impl<U, T>(0)
- > {};
- #else
- template<typename Base, typename Derived, typename tag>
- struct is_virtual_base_of_impl
- {
- BOOST_STATIC_CONSTANT(bool, value = false);
- };
- template<typename Base, typename Derived>
- struct is_virtual_base_of_impl<Base, Derived, true_type>
- {
- union max_align
- {
- unsigned u;
- unsigned long ul;
- void* v;
- double d;
- long double ld;
- #ifndef BOOST_NO_LONG_LONG
- long long ll;
- #endif
- };
- #ifdef __BORLANDC__
- struct boost_type_traits_internal_struct_X : public virtual Derived, public virtual Base
- {
- boost_type_traits_internal_struct_X();
- boost_type_traits_internal_struct_X(const boost_type_traits_internal_struct_X&);
- boost_type_traits_internal_struct_X& operator=(const boost_type_traits_internal_struct_X&);
- ~boost_type_traits_internal_struct_X()throw();
- max_align data[4];
- };
- struct boost_type_traits_internal_struct_Y : public virtual Derived
- {
- boost_type_traits_internal_struct_Y();
- boost_type_traits_internal_struct_Y(const boost_type_traits_internal_struct_Y&);
- boost_type_traits_internal_struct_Y& operator=(const boost_type_traits_internal_struct_Y&);
- ~boost_type_traits_internal_struct_Y()throw();
- max_align data[4];
- };
- #else
- struct boost_type_traits_internal_struct_X : public Derived, virtual Base
- {
- boost_type_traits_internal_struct_X();
- boost_type_traits_internal_struct_X(const boost_type_traits_internal_struct_X&);
- boost_type_traits_internal_struct_X& operator=(const boost_type_traits_internal_struct_X&);
- ~boost_type_traits_internal_struct_X()throw();
- max_align data[16];
- };
- struct boost_type_traits_internal_struct_Y : public Derived
- {
- boost_type_traits_internal_struct_Y();
- boost_type_traits_internal_struct_Y(const boost_type_traits_internal_struct_Y&);
- boost_type_traits_internal_struct_Y& operator=(const boost_type_traits_internal_struct_Y&);
- ~boost_type_traits_internal_struct_Y()throw();
- max_align data[16];
- };
- #endif
- BOOST_STATIC_CONSTANT(bool, value = (sizeof(boost_type_traits_internal_struct_X) == sizeof(boost_type_traits_internal_struct_Y)));
- };
- template<typename Base, typename Derived>
- struct is_virtual_base_of_impl2
- {
- typedef boost::integral_constant<bool, (boost::is_base_of<Base, Derived>::value && !boost::is_same<Base, Derived>::value)> tag_type;
- typedef is_virtual_base_of_impl<Base, Derived, tag_type> imp;
- BOOST_STATIC_CONSTANT(bool, value = imp::value);
- };
- } // namespace detail
- template <class Base, class Derived> struct is_virtual_base_of : public integral_constant<bool, (::boost::detail::is_virtual_base_of_impl2<Base, Derived>::value)> {};
- #endif
- template <class Base, class Derived> struct is_virtual_base_of<Base&, Derived> : public false_type{};
- template <class Base, class Derived> struct is_virtual_base_of<Base, Derived&> : public false_type{};
- template <class Base, class Derived> struct is_virtual_base_of<Base&, Derived&> : public false_type{};
- #ifdef BOOST_MSVC
- #pragma warning( pop )
- #endif
- } // namespace boost
- #endif
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