https://svn.boost.org/trac10/ticket/10129 <p> Boost.Bind default placeholders (anonymous namespace)<code>::_1</code>, (anonymous namespace)<code>::_2</code> etc. can be not used either by directly creating objects of type <code>boost::arg&lt;1&gt;</code>, <code>boost::arg&lt;2&gt;</code> etc. or by resorting to user-defined placeholders properly labelled as such via <code>boost::_is_placeholder</code>. This comes handy when <code>BOOST_BIND_NO_PLACEHOLDERS</code> is set and in general when the <code>_1</code> syntax is not welcome for whatever reason. </p> <p> The problem is that both <code>boost::arg&lt;N&gt;</code> and <code>boost::is_placeholder</code> are not documented, i.e. they officially do not exist. This, in particular, renders Boost.Bind effectively unusable when <code>BOOST_BIND_NO_PLACEHOLDERS</code> is in effect. </p> <p> This is a request that these constructs be documented. More info on the subject on </p> <p> <a class="ext-link" href="http://lists.boost.org/Archives/boost/2014/03/212333.php"><span class="icon">​</span>http://lists.boost.org/Archives/boost/2014/03/212333.php</a> </p> en-us /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/10129 Trac 1.4.3