Hi David, Thanks for your suggestions. David Abrahams wrote:
template <typename P> double area(const P& polyon, typename boost::enable_if_c<geometry_type<P>::type == TYPE_POLYGON>::type* = 0)
This works perfectly and distinguishes all geometry types at compile time, as long as the library or the developer provides the meta function geometry_type<T>::type which is currently implemented as an enumeration of TYPE_POINT, etc.
Seems like you might be better off using tag dispatching... or something like
http://article.gmane.org/gmane.comp.lib.boost.devel/120718 http://article.gmane.org/gmane.comp.lib.boost.devel/120728
You are right. The system using enable_if_c works and is recommended by the boost doc of enable_if :-). (quote: The enable_if family of templates is a set of tools to allow a function template or a class template specialization to include or exclude itself from a set of matching functions or specializations based on properties of its template arguments) But tag dispatching works perfectly as well and I see that there are more advantages.
We therefore use BOOST_CONCEPT_REQUIRES instead of _ASSERT in such cases.
I think you mean the opposite, right?
Sure, the opposite, sorry for the mistake. Regards, Barend