Wasn't this macro a VC6 workaround?
As a first step we could just add an empty macro and see if anything today actually needs it.
That's what I was planning, these macros are all basically superfluous now.
I am seeing in MPL empty_base.hpp:
#include
but this file does not exist in type_traits Version2.
I've added back "do nothing much" versions of those missing files. A lot more should build now. However, there are a couple of show-stoppers I don't know how to solve: 1) boost::integral_constant is no longer a model of mpl's integral_constant: http://www.boost.org/doc/libs/1_57_0/libs/mpl/doc/refmanual/integral-constan... As a result all of function_types lib is broken. I guess one could argue that if you want to do arithmetic on integral_constant's then one should use MPL all the way through. But it's a big breaking change. 2) There are few places (well, myself in multiprecision lib) where folks do dispatch on multiple conditions: do_something(mpl::true_ const&, mpl::true_ const&){} do_something(mpl::true_ const&, mpl::false_ const&){} template <bool B> do_something(mpl::true_ const&, mpl::bool_<B> const& {/*catch all case*/} Then: do_something(trait1<T>(), trait2<T>()); The problem here is that the final catch all case can not be found unless trait2 actually inherits from mpl::bool_ rather than being merely convertible to it. John.