Re: Using policy based design with Singleton template class

red floyd <no.spam@here.dude>
18 Oct 2006 15:18:20 -0400
YellowMaple wrote:

Is there any elegant way for a class to derive from a template
singleton class (e.g. Meyer's singleton) yet still allow for
flexibility via policies? That is, what I want to do is something like

template <template <typename> class MyPolicy>
class Foo
     : public Singleton<Foo>
     , public MyPolicy<Foo>

It would be nice to have allow clients the flexibility that comes with
policies, yet to be able to enforce uniqueness through the singleton
design. I am unable to come up with a simple solution that doesn't
have any loop holes.

Alexandrescu discusses this somewhat in Modern C++ Design.

I don't have the book handy, but I think it's something like:

struct DefaultPolicy
   // policy interface

template<typename T, typename Policy = DefaultPolicy>
class Singleton
   // Singleton interface

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