Basing on discussions with Jason, I'm filing this PR, distilled from a typical
library-only implementation of std::is_convertible instantiated with D and A,
where A is an ambiguous base of D.
As a matter of fact, I'm personally not *completely* sure that SFINAE should
apply here, but I'm tempted to believe than for is_convertible one cannot do
much better than the below at the library-only level - I just checked that
boost::is_convertible behaves exactly the same. In any case, better double
checking with Jason:
struct A { };
struct B
: public A { };
struct C
: public A { };
struct D
: public B, public C { };
template<typename _From, typename _To>
class mini_is_convertible
{
typedef char __one;
typedef struct { char __arr[2]; } __two;
static __one __test(_To);
static __two __test(...);
public:
static const bool __value = sizeof(__test(_From())) == 1;
};
void foo()
{
mini_is_convertible<D, A>::__value;
}
--
Summary: Problem with SFINAE and ambiguous base
Product: gcc
Version: 4.6.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: paolo dot carlini at oracle dot com
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44896
