On Thu, 2008-01-10 at 16:57 -0500, Michael Fawcett wrote:
Traits classes are far better than nested typedefs, because one can always specialize a traits class for an existing type---even if you can't modify the type because it is built-in or comes from another library that you can't modify.
This has always been my thinking, but to play devil's advocate, what about providing an adapter class around that type that you can't modify? To answer my own question, it provides a much larger burden on the user of your library (wrap all instances with wrapper type when using my generic algorithms vs. specializing one traits struct).
Exactly. An adapter class is always an option (whether or not the generic algorithm uses traits), but it's a last-resort option because it often requires more code and more maintenance than specializing traits.
// Completely traits template <typename T> typename node_traits<T>::data_type *data(T *node) { boost::function_requires<NodeConcept>(); return slist_node_traits<T>::data(node) }
and, if you suggest using all traits, would Node Concept be reduced to simply checking to see if node_traits was fully specialized?
Using all traits is extremely hard, because so many things happen implictly in C++---implicit conversions, copy constructions, etc.. But yes, if you used only traits, checking for a fully specialized node_traits (with the right signatures!) would work. - Doug