boost::arg and boost::is_placeholder not documented

[Joaquín M López Muñoz]

Boost.Bind default placeholders (anonymous namespace)::_1, (anonymous namespace)::_2 etc. can be not used either by directly creating objects of type boost::arg<1>, boost::arg<2> etc. or by resorting to user-defined placeholders properly labelled as such via boost::_is_placeholder. This comes handy when BOOST_BIND_NO_PLACEHOLDERS is set and in general when the _1 syntax is not welcome for whatever reason.

The problem is that both boost::arg<N> and boost::is_placeholder are not documented, i.e. they officially do not exist. This, in particular, renders Boost.Bind effectively unusable when BOOST_BIND_NO_PLACEHOLDERS is in effect.

This is a request that these constructs be documented. More info on the subject on

​http://lists.boost.org/Archives/boost/2014/03/212333.php