General talk about software patterns

["Eric Y. Theriault" <eric AT eyt.ca>]

E. Segura wrote:

> When using the Singleton pattern...
>
> Who should delete the _instance?
>
> Should I ask for it and delete it myself?
> ( i.e. delete(myClass::getInstance()) ????? )
>
> or the class should keep a "reference count" and other
> classes should inform when the don't use the instance
> reference anymore.
>  

John Vlissides has written a great article on the topic, entitled "To 
Kill a Singleton", which I believe you can get at 
http://www.research.ibm.com/designpatterns/pubs/ph-jun96.txt .  Andre 
Alexandrescu's Modern C++ Design book also has a good treatment of the 
topic, where he basically allows this to be specified by a policy.  In 
other words, the users of the singleton object should be (more or less) 
oblivious to how it is constructed and destroyed.

I would avoid the delete mechanism above, since this assumes that the 
pointer is allocated by new.  In actuality, the value returned by 
getInstance() is not necessarily allocated by new, as Alexandrescu 
refers to the Meyers Singleton, where the singleton object is a static 
variable.

The above two resources offer are excellent insight to this issue.



eyt*
--
Eric Y. Theriault
http://www.eyt.ca