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Merge branch 'hotfix/is_virtual_base_of' of https://github.com/csernib/type_traits into pr31

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jzmaddock
2018-05-08 18:59:29 +01:00
parent 01f9a0b43a 7f792f96c9
commit 2cc2697e53
1 changed files with 26 additions and 62 deletions
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88
include/boost/type_traits/is_virtual_base_of.hpp
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@ -1,4 +1,5 @@
// (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).
@ -9,7 +10,6 @@
#define BOOST_TT_IS_VIRTUAL_BASE_OF_HPP_INCLUDED
#include <boost/type_traits/is_base_of.hpp>
#include <boost/type_traits/is_same.hpp>
namespace boost {
namespace detail {
@ -22,70 +22,34 @@ namespace detail {
#pragma GCC system_header
#endif
template<typename Base, typename Derived, typename tag>
template<class Base, class Derived>
struct is_virtual_base_of_impl
{
BOOST_STATIC_CONSTANT(bool, value = false);
};
template<class From, class To>
struct can_cast
{
typedef char YES;
typedef struct { char x[2]; } NO;
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)));
};
// 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<unsigned = sizeof((To*)((From*)(0)))> static YES test(int*);
static NO test(...);
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);
BOOST_STATIC_CONSTANT(bool, value = (sizeof(test(nullptr)) == sizeof(YES)));
};
// 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.
BOOST_STATIC_CONSTANT(bool, value = (boost::is_base_of<Base, Derived>::value && can_cast<Derived, Base>::value && !can_cast<Base, Derived>::value));
};
#ifdef BOOST_MSVC
@ -94,7 +58,7 @@ struct is_virtual_base_of_impl2
} // 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)>{};
template <class Base, class Derived> struct is_virtual_base_of : public integral_constant<bool, (::boost::detail::is_virtual_base_of_impl<Base, Derived>::value)>{};
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{};