Rob Stewart wrote:
IOW, if basic_singleton requires that the Creator template argument derive from creator_base, and creator_base uses a noninstantiable technique, then the client cannot create a Creator instance, so the only way to create an instance of type T is if T permits it.
Exactly.
Provided that using basic_singleton<T> places no contrary burdens on T such that basic_singleton<T> controls (a) common, Singleton instance(s), yet other T's can be instantiated directly, it sounds good. Unfortunately, the functionality you described was provided by singleton_base suggests that this isn't the case.
Am I missing something still?
The functionality is provided in terms of a member class, called pointer. If T derives from singleton < T >, client code can use T::pointer instances to get at the singleton instance. If T does not derive from singleton < T >, client code must use singleton < T
::pointer instances to refer to the singleton instance.
-Jason