I have checked in a boostification/typetraitification of this idea. It can be found in boost/serialization/is_virtual_base_of.hpp I have tested it as used in the serialization library with MSVC compilers and gcc. With gcc it doesn't indeed create an annoying warning. I would like to see the type_trait gurus to: a) look at this b) see if this gcc warning can be suppressed c) if its OK move it to the type_traits library and out of the serialization librar d) maybe add a separate test. e) and promote to the next release branch since I prefer to run my local tests against the next release branch. Thank you very much. Robert Ramey Daniel Frey wrote:
On 08.03.2009, at 11:02, John Maddock wrote:
If not is there a way to make such a thing? Can't think of a method off the top of my head, but Boosters are a clever lot so you never know....!
One can check if the size changes when creating another class:
template< typename D, typename B > struct is_virtual_base_of { struct X : D, virtual B {}; enum { value = sizeof(X)==sizeof(D) }; };
template< typename T > struct is_virtual_base_of< T, T > { enum { value = false }; };
it triggers some warnings with GCC in my experiments when a base class is *not* virtual, but it seems to detect virtual bases just fine. Disclaimer: It's a start, nothing more. I have no idea how other compilers (even other compiler versions of GCC other than 4.3.2) will react on it, etc.
Regards, Daniel
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