and_<true_>::type is false_

[mstefanro]

It is probably a good idea to make and_<true_>::type be true_, or throw a compiler error, or at least fix the documentation at http://www.boost.org/doc/libs/1_43_0/libs/mpl/doc/refmanual/and.html such that this unusual behavior is documented.

[Steven Watanabe]

Hmmm. The fact that this even compiles is an artifact of the way mpl::na is implemented. and_ is only intended to take two or more arguments.

[Bryce Adelstein Lelbach]

Confirmed, this is still a problem, possibly a problem with other binary logical operations too. I think we need to prohibit an unary and_ entirely. This reproduces the problem:

#include <boost/mpl/assert.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/mpl/and.hpp>

int main (void) {
  using boost::mpl::and_;
  using boost::mpl::true_;

  BOOST_MPL_ASSERT((and_<true_>));
}