Re: Am I or Alexandrescu wrong about singletons?

I do the same as him. This is what he does.

Here's Singleton.h

00717 template
00718 <
00719 typename T,
00720 template <class> class CreationPolicy = CreateUsingNew,
00721 template <class> class LifetimePolicy = DefaultLifetime,
00722 template <class, class> class ThreadingModel =
00722b LOKI_DEFAULT_THREADING_NO_OBJ_LEVEL,
00723 class MutexPolicy = LOKI_DEFAULT_MUTEX
00724 >
00725 class SingletonHolder
00726 {
00727 public:

00733 static T& Instance();

00744 typedef typename
00744b ThreadingModel<T*,MutexPolicy>::VolatileType
00744c PtrInstanceType;
00745 static PtrInstanceType pInstance_;

00747 };

[...]

00775 // SingletonHolder::Instance
00777
00778 template
00779 <
00780 class T,
00781 template <class> class CreationPolicy,
00782 template <class> class LifetimePolicy,
00783 template <class, class> class ThreadingModel,
00784 class MutexPolicy
00785 >
00786 inline T& SingletonHolder<T, CreationPolicy,
00787 LifetimePolicy, ThreadingModel, MutexPolicy>::Instance()
00788 {
00789 if (!pInstance_)
00790 {
00791 MakeInstance();
00792 }
00793 return *pInstance_;
00794 }

Here's Threads.h containing ThreadingModel.

00252 template < class Host, class MutexPolicy =
00252b LOKI_DEFAULT_MUTEX >
00253 class ObjectLevelLockable
00254 {

00299 typedef volatile Host VolatileType;

00305 };

If you look at row 744b you see that he passes T* to ThreadingModel. If
you then look at row 299 you see that his VolatileType becomes a
volatile T*.

He and me then do the exact same thing on row 793,
initializing a T& with a volatile T.