[boost] Nullable types

Subject: [boost] Nullable types
From: Bjorn Reese (breese_at_[hidden])
Date: 2013-07-13 07:56:48

It seems like different Boost libraries use different nullable types.

   * Optional uses boost::none
   * Tribool uses boost::logic::indeterminate_keyword_t
   * Tuple uses boost::tuples::null_type
   * Variant uses boost::blank

And there are possibly more.

What are your opinions about unifying these?