is_base_of<B, D> should work ehen B is incomplete

[akrzemi1]

The Standard ([meta.rel]) requires that in is_base_of<B, D> D must be a complete type, but it does not require the same of B. This makes sense, because if we compare a complete type D and an incomplete type B, the former is surely not derived from the latter.

In contrast, boost::is_base_of imposes an additional constraint that B must also be complete:

http://www.boost.org/doc/libs/1_60_0/libs/type_traits/doc/html/boost_typetraits/reference/is_base_of.html

Can you remove this extra constraint? It appears to be spoiling one Boost.Optional tests:

http://www.boost.org/development/tests/master/developer/output/oracle-sparc-S2-12-5-cpp11-boost-bin-v2-libs-optional-test-optional_test-test-sun-12-5_cpp11-release-threading-multi.html

[Mike <vigorous.activity@…>]

Checked 1.55 boost version, works with incomplete B.

[John Maddock]

I've been having a look at this and:

• There is no restriction on B being complete as long as we have a working compiler intrinsic that supports this.
• The Oracle compiler supports the __oracle_is_base_of intrinsic, but it's use is even more restricted/broken. So we don't use it, as it makes things even worse than they are already.

Sorry, but I don't see any easy way to fix this.