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<int, Int>::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<Int, int>::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.