On Wed, Mar 16, 2011 at 3:45 PM, Mathias Gaunard <mathias.gaunard@ens-lyon.org> wrote:
On 16/03/2011 19:39, John Maddock wrote:
* Remove the concept related macros. * Tighten up most of the C++0x related tests, with the result that some C++0x features that were previously enabled are no longer - this may also cause the Boost.Config tests to fail on some platforms. * Some C++0x features that were not previously enabled are now - because they were passing the Boost.Config tests - there's at least one case where this is causing regressions in other libraries - if any more pop up please let me know ASAP!
Any reason why decltype on MSVC10 is still not enabled?
If someone tells me that this issue: http://lists.boost.org/Archives/boost/2010/04/164645.php is fixed then fine, otherwise it appears to be a lot trouble,
I wasn't aware of this issue. But doesn't it only affect result_of, with decltype still usable in practice for other things?
result_of is little more than a synonym for decltype; e.g. for types F and T, result_of<F(T)>::type evaluates to decltype(declval<F>()(declval<T>())). The issue here is that msvc runs out of heap space if decltype is used with a call expression in a context in which the type of the call expression is incomplete. https://connect.microsoft.com/VisualStudio/feedback/details/548883/c-use-of-... However, as far as I understand, this usage is not valid C++0x, since a call expression is still required to have a complete type. So, I don't believe this issue alone merits disabling decltype on msvc. In the future, if the complete type requirement is removed from the standard, then I expect Microsoft will try to comply. So, the question is whether the current msvc decltype is close enough to the current standard. With regard to boost::result_of, users must explicitly enable the decltype version by defining BOOST_RESULT_OF_USE_DECLTYPE, and either way, the TR1 version is always available as boost::tr1_result_of, which, I believe, Proto uses. So from the perspective of boost::result_of, I see no reason to deny msvc users the option of enabling decltype. Daniel Walker