concept_check and B&N trick

From: Eric Ford (eford_at_[hidden])
Date: 2001-10-02 18:24:52

I ran into problems using BOOST_CLASS_REQUIRES in conjunction with the
base class in the Barton-Nackman trick/Curiously recursive template
technique. 

I want to require functions that take the derived type as an
argument.  So I declare a variable of the derived at struct level in
the concept class, but then g++ (2.95) complains about it being an
invalid use of undefined type... forward declaration...  .  Is there a
way to make this work?  If so, does anyone have/know of an example I
can see how to order things to make it work?

Thanks,
E