[boost] singleton usage

From: Jason Hise (chaos_at_[hidden])
Date: 2005-02-13 19:20:07

I recently discovered that my singleton could potentially be used in a 
way other than as a base class.  For example, to create and use a 
singleton instance of a class which could have other ordinary instances 
as well, one could just do:

class Example
{
public:
    void foo (  )
    {
    }
};

// elsewhere...

singleton < Example >::pointer ptr;
ptr->foo (  );

In addition, one could make a singleton who's instance refers to another 
class by deriving from a singleton of that type, as follows (using the 
Example above):

class ExampleSingleton : public singleton < Example >
{
private:
    ExampleSingleton (  );
    ~ ExampleSingleton (  );
};

which would essentially create a shorter name for singleton < Example >.

I need opinions: should this type of usage be allowed, or should I find 
some way to make it fail to compile?  If allowed, should it be 
encouraged and/or documented?

-Jason