I'm continuing to refine a boost::unique_ptr emulation and testsuite. One thing I've just uncovered is that I'm hitting a brick wall with is_convertible and move-only deleters used within the unique_ptr move constructor. The problem is that boost::is_convertible<From, To> assumes From is an lvalue. is_convertible<Deleter, Deleter> gets instantiated and it is all over. I've modified my copy of is_convertible (without really knowing what I'm doing) like so: Index: is_convertible.hpp =================================================================== --- is_convertible.hpp (revision 50433) +++ is_convertible.hpp (working copy) @@ -119,6 +119,8 @@ struct any_conversion { template <typename T> any_conversion(const volatile T&); + template <typename T> any_conversion(volatile T&); + template <typename T> any_conversion(const T&); template <typename T> any_conversion(T&); }; @@ -131,8 +133,8 @@ template <typename From, typename To> struct is_convertible_basic_impl { - static From _m_from; - static bool const value = sizeof( detail::checker<To>::_m_check(_m_from, 0) ) + static From _m_from(); + static bool const value = sizeof( detail::checker<To>::_m_check(_m_from(), 0) ) == sizeof(::boost::type_traits::yes_type); }; @@ -291,7 +293,8 @@ template <typename From, typename To> struct is_convertible_impl { - typedef typename add_reference<From>::type ref_type; +// typedef typename add_reference<From>::type ref_type; + typedef From ref_type; BOOST_STATIC_CONSTANT(bool, value = (::boost::type_traits::ice_and< ::boost::type_traits::ice_or< This hits just the part targeting gcc. The intent is that in boost::is_convertible<From, To> From is now considered an rvalue (unless From is a (lvalue) reference type). This makes my test case happy. I can now move construct a unique_ptr with a move-only deleter. Fwiw, this definition of is_convertible is consistent with std::is_convertible in N2800:
In order to instantiate the template is_convertible<From, To>, the following code shall be well formed:
template <class T> typename add_rvalue_reference<T>::type create(); To test() { return create<From>(); }
[ Note: This requirement gives well defined results for reference types, void types, array types, and function types. -- end note ]
I've got a much more refined unique_ptr testsuite on the way which will contain the unique_ptr header and test case for this (not there yet, I'll post when it is). -Howard