On 11/08/12 21:26, Lorenzo Caminiti wrote:
On Wed, Aug 8, 2012 at 8:59 PM, John Bytheway <jbytheway+boost@gmail.com> wrote:
I have been tracking down an issue with some of my code which compiles fine with gcc but not clang. It manifested as a failure in Boost.Parameter but I eventually pinned it down to an inconsistency in the behaviour of boost::is_convertible. The following program
For curiosity, when using Boost.Parameter what error did you see? (Even if I understand the error was ultimately not there.)
I've investigated further and am less sure that it was Boost.Parameter's fault. I attach my test case. In particular: BOOST_PARAMETER_CONSTRUCTOR( B, (constructor_impl), tag, (required (in_out(tag_1), (A&)) ) ) On closer reading of the Boost.Parameter docs I guess it is probably not allowed to pass a reference type as an type requirement, although again it's not entirely clear. I guess (not sure) that when I first wrote this code I used A in place of A&, which fails because A is non-moveable, and when Boost.Parameter checks is_convertible<A,A>, which is false, it thinks that the call is not a match. With the implementation of is_convertible at that time, switching to A& made everything work, because then it was checking is_convertible<A,A&>, which was true. Now my workaround no longer works, and I wonder: what is the proper way to capture a reference to a non-moveable type in a Boost.Parameter argument? Perhaps the A& technique I used is supposed to work but no longer does because of the changed meaning of boost::is_convertible after Boost 1.46 (as mentioned by Michel elsewhere)? John