Is there any other functionality that should be added? Specifically, is it sufficient to enforce that singletons are created in a specific order before main and destroyed in the reverse order after main (using dependency instances), or should I provide some way to support alternate lifetimes (ex: create on first reference to instance)?
Is there any interest in adding this library to Boost?
Well, one thing that would be interesting to support is the ability to force the destruction and/or deconnection of all objects referenced from a singleton... For example, when programming with COM (ActiveX), we might have a bunch of objects created by a singleton that must be destroyed before we call CoFreeUnusedLibraries() and/or CoUninitialize(). Also, with multiples DLLs, we typically need to ensure that all references are destroyed before the system unload the DLL. When there are complex depedencies, the system might not knows which DLL to unload first and if some of them have dynamic links to object in other DLL (via the singleton), the application might crash when exiting. This might also be interesting in some situations like a singleton is associated with a document (or maybe a window). So what is needed to cover such cases is the ability to set the object in a "destroying" state. A solution that could work in some situation would be something similar to: Singleton::Deconnect() { if (object) { object->Deconnect(); } } Well, the way to do the deconnection on the object hold by the singleton would not be an hard-coded member but something that would be settable by a policy class or some other template mean (for example, type trait). Another reason that one might want to be able to control when the destruction occurs is that it can allows all code to be executed from a try/catch block in main (so the application can report the error instead of the OS). Philippe