Scott Woods wrote:
<>...one day you are asked to produce a self-verifying version of your switch that runs two instances side-by-side. Or you are asked to do some call-setup performance testing, i.e. you need to run two instances of your PBX against each other. Or you need to perform soak testing that needs 6 instances in a single executable. And so on. Should the abstraction known as Singleton truly preclude there ever being more than 1 instance?
This is an interesting point. Perhaps the derived template class could be templated itself to take one parameter, an int. Then a new instance of the singleton could be referenced at any time by simply referring to the singleton type with a different unique ID for the template parameter. The field could default to zero for normal usage as a singleton. Ex: template < int I = 0 > class Important : Singleton < Important > { protected: Important ( ) { } ~ Important ( ) { } public: // important stuff here }; void TestWithThreeInstances ( ) { Important < 0 > :: Pointer instZero = Important < 0 > :: GetInst ( ); Important < 1 > :: Pointer instOne = Important < 1 > :: GetInst ( ); Important < 2 > :: Pointer instTwo = Important < 2 > :: GetInst ( ); // do testing here } -Jason