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Implement std::is_base_of for the case where we don't have a compiler

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intrinsic. This relies upon the fact that overload resolution does not check
access and ambiguity for a derived-to-base conversion. This passes all
is_base_of tests in the test suite.


git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@170662 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Richard Smith 2012-12-20 04:20:28 +00:00
parent a46482e8bb
commit b2f2b68143
1 changed files with 22 additions and 1 deletions

23
include/type_traits

@ -617,7 +617,28 @@ struct _LIBCPP_VISIBLE is_base_of
#else // __has_feature(is_base_of)
#error is_base_of not implemented.
namespace __is_base_of_imp
{
template <class _Tp>
struct _Dst
{
_Dst(const volatile _Tp &);
};
template <class _Tp>
struct _Src
{
operator const volatile _Tp &();
template <class _Up> operator const _Dst<_Up> &();
};
template <size_t> struct __one { typedef char type; };
template <class _Bp, class _Dp> typename __one<sizeof(_Dst<_Bp>(declval<_Src<_Dp> >()))>::type __test(int);
template <class _Bp, class _Dp> __two __test(...);
}
template <class _Bp, class _Dp>
struct _LIBCPP_VISIBLE is_base_of
: public integral_constant<bool, is_class<_Bp>::value &&
sizeof(__is_base_of_imp::__test<_Bp, _Dp>(0)) == 2> {};
#endif // __has_feature(is_base_of)