Re: [boost] pure virtual singleton

From: Jason Hise (chaos_at_[hidden])
Date: 2005-03-26 15:50:30

Rob Stewart wrote:

>I contend that you can provide a mechanism whereby clients can
>ensure their type can only be instantiated by the Singleton
>framework, but don't require that.
>
I already do :)  You can use a type deriving from the singleton if you 
want true singleton behavior, or you can use a typedef if you want one 
globally managed resource and any number of local resources.

class A : public singleton < A > { /*...*/ }; // only the singleton 
instance can exist
class B { /*...*/ }; // can create any number of B instances
typedef singleton < B > global_b; // but global_b manages the lifetime 
of one global B instance.

There is a multiton for cases when you need multiple global instances 
that uses key based identification, and alternately you can derive a 
different type from B for each global instance you want managed.

class Printer { /*...*/ };

class PrinterA : public Printer, public singleton < PrinterA > {  };
class PrinterB : public Printer, public singleton < PrinterB > {  };

-Jason