David Abrahams <dave <at> boost-consulting.com> writes:
Rene Rivera <grafik.list <at> redshift-software.com> writes:
It's an ODR thing. If you then use the parameter names in a function template that's not in an unnamed namespace but _is_ in multiple TU's, you have technically violated the ODR.
In general, types in header files had better stay out of the unnamed namespace.
In fact, it looks like to be really safe from ODR violations we need to require the keyword objects to be declared as _references_ in the unnamed namespace using the unique_instance trick, per http://thread.gmane.org/gmane.comp.lib.boost.devel/126455 because a function template using named parameters and instantiated in different translation units might otherwise use different objects. It's very tempting to ignore this problem, because IMO it will *never* cause a problem in practice, and because it complicates the usage and documentation of the parameter library. We also need someplace to put unique_instance. It's too general to go in boost::parameter and it's not suitable for boost::detail since users have to touch it. Any helpful ideas about all this would be appreciated, especially if you can find standard text that makes it all go away ;-) For more context, please see my Nov 16th reply to Rene in http://thread.gmane.org/gmane.comp.lib.boost.devel/113158 GMane's posting nanny won't let me quote very much. -- Dave Abrahams Boost Consulting http://www.boost-consulting.com