on Fri Nov 25 2011, Robert Kawulak <robert.kawulak-AT-gmail.com> wrote:
From: Stewart, Robert
- The implementation of assignable_archetype defines private default and copy constructors, so for example assignable_archetype<copy_constructible_archetype<>> will not actually be copy constructible. The same for convertible_to_archetype and convertible_from_archetype, but additionally with copy assignment. Is this by purpose?
I should think that's by design. The archetypes are to validate a particular concept checking class, so a copyable or default constructible archetype for Assignable would be wrong.
I wouldn't say it's wrong. If you can combine several concepts, you should be able to combine the corresponding archetypes too. If your template requires more than one concept (e.g., a type that is BOTH copyable AND assignable), then without the ability of chaining you would have to write your own archetypes in all but the most trivial cases.
I think the problem is that C++03 doesn't let you define copyability and assignability "additively," and offers no way to detect those capabilities so we can decide not to subtract them. -- Dave Abrahams BoostPro Computing http://www.boostpro.com