Folks, I suspect we may have unintentionally backed ourselves into a
corner with is_convertible/is_constructible.
While trying to fix https://svn.boost.org/trac/boost/ticket/11922 I
found I needed to SFINAE-out some conversion operators when the
conversion already exists (as an implicit constructor in the target
type). So far so easy, but consider:
class Int {
public:
Int(const int& i) {};
Int(const Int& i) = delete;
};
static_assert(is_convertible::value, "Ooops");
Now you would think this would pass right? But it doesn't (at least on
GCC and clang), and this is true for both boost:: and std:: type_traits
and appears to be an unintended side effect of the way is_convertible is
defined, that a valid copy constructor is required on the target type.
Of course:
is_constructible::value
is true, but that also catches explicit constructors.
So... have we backed ourselves into a corner or do we still have a way
to test for implicit-constructibilty that doesn't also require
copy-constructibility on the target type?
Thanks, John.
