On Feb 14, 2010, at 2:55 PM, vicente.botet wrote:
The implementation is based on whether the base type is polymorphic, not whether the base type is_virtual_base_of<B,D>. I have replaced
template<class U> static T cast(U * u){ typedef BOOST_DEDUCED_TYPENAME mpl::eval_if< BOOST_DEDUCED_TYPENAME mpl::and_< mpl::not_<is_base_and_derived< BOOST_DEDUCED_TYPENAME remove_pointer<T>::type, U
, mpl::not_<is_base_and_derived< U, BOOST_DEDUCED_TYPENAME remove_pointer<T>::type
, mpl::identity<cross>, mpl::identity<linear> ::type typex; return typex::cast(u); } by template<class U> static T cast(U * u){ typedef BOOST_DEDUCED_TYPENAME mpl::eval_if< is_virtual_base_of<U, BOOST_DEDUCED_TYPENAME remove_pointer<T>::type>, mpl::identity<cross>, mpl::identity<linear> ::type typex; return typex::cast(u); }
And it work also. But now dynamic_cast is used only if U is virtual_base_of T.
I don't think this change is correct, as it will result in using static_cast in an actual cross-cast situation, i.e. when there is no base/derived relationship between U and T, but they have a common derived type of which the value being cast is an instance. However, it seems to me that there is a bug in the existing smart_cast implementation, in that it may incorrectly attempt to use static_cast in the case where U is a virtual_base_of T. I think the correct fix is to leave the existing derivation test in place, but augment it with the is_virtual_base_of test, i.e. mpl::or_ the existing test for cross-cast (T and U have no base/derived relationship) with the is_virtual_base_of test.