id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
3114	Modified interface to allow even lazier return types for defaults	Jeremiah Willcock	Jeremiah Willcock	There are some use cases where the return type of operator() in a default computation class is not valid in some cases when that default is not used.  The current interface to such classes does not allow that case; see the message at http://lists.boost.org/Archives/boost/2009/05/152009.php for more information.  The attached patch allows a special member type (that must be void) to be used to change the interface to pass a single int argument to operator(), while keeping the old no-parameter interface for function objects without the special tag.  The tag could also have been implemented as a traits class used with enable_if.  The patch passes all of the Boost.Parameter tests except two (which appear to freeze up).  I only changed the normal path through the code, and not the compatibility code which I am unable to test.  A test for the new functionality added by the patch is also attached.	Feature Requests	new	Boost 1.42.0	parameter	Boost 1.38.0	Problem