On Friday 13 June 2014 09:27:04 Eric Niebler wrote:
I am in favor of adding an mpl::tag_of metafunction which retrieves the tag type of the passed mpl entity.
I think, mpl::tag already implements that. See mpl/tag.hpp.
It can be specialized for std::integral_constant to do the right thing. In addition, it would fix the issues raised here:
http://lists.boost.org/Archives/boost/2009/01/147045.php
and here:
https://svn.boost.org/trac/boost/ticket/7192
I think in the C++11 world, boost type_traits should *all* inherit from std::true_type. That's easily accomplished by aliasing mpl::true_ to std::true_type. It fixes everything.
Well, technically that would still be a breaking change, even though a relatively safe one. I think if the goal is to add support for std::integral_constant to MPL, it can be achieved with a less radical solution.