On 28 Jun 2017, at 16:52, dariomt@gmail.com wrote:
2017-06-27 20:05 GMT+02:00 d25fe0be@outlook.com <d25fe0be@outlook.com>: Sorry I missed John's reply..
I believe John is right, without C++11 a fully conforming is_convertible seems not to be implementable (I didn't find a way to remove `_m_check` taking the inaccessible base as a parameter from the overload set.), hence 'your own `is_convertible`' seems not to be feasible either.
Thank you John for pointing this out, and sorry for the noise.
Thanks for the follow up.
So the only workaround with 1.64 is to get rid of the private inheritance, right?
I'm afraid yes.
Anyway, my test case used to work in older versions of Boost. I'm not sure about what changed between 1.61 and 1.62, if it's a change in type_traits or a change in variant. Would it be possible to recover the lost functionality in 1.65?
I think the change was introduced by commit [https://github.com/boostorg/variant/commit/b3650685f941a0c35cadfd878a185f274...], which tried to solve ticket #11602 [https://svn.boost.org/trac10/ticket/11602]. I don't know how can both #11602 and the issue here be solved at the same time. CC'ing Antony. Perhaps we can test for convertibility only if C++11 is available, and leave #11602 unsolved in C++03 (as there're still corner cases not solved as of now, see below)? --- As `boost::is_constructible` triggers a hard error when testing a class and its privately parent, the following code fails the compilation as well (both before (because of #11602) and after (because of the hard error triggered by `boost::is_convertible`) commit b3650685f941a0c35cadfd878a185f274e132788): ``` #include <boost/variant.hpp> class A {}; class B : private A {}; void foo(boost::variant<A> v) {} void foo(boost::variant<B> v) {} int main() { B b; foo(b); } ```