https://svn.boost.org/trac10/ticket/4613 <p> If a default Boolean value isn't used in extracting the value from the <a class="missing wiki">ArgumentPack</a> a compile error occurs. That means that this code compiles "m_name(args[_name | false])" but "m_name(args[_name])" doesn't. A code example can be found in this boost thread. </p> <p> <a class="ext-link" href="http://old.nabble.com/-parameter--Weird-behavior-with-bools-td29539068.html"><span class="icon">​</span>http://old.nabble.com/-parameter--Weird-behavior-with-bools-td29539068.html</a> </p> en-us /htdocs/site/boost.png https://svn.boost.org/trac10/ticket/4613 Trac 1.4.3