Extending Python with C++ singleton pattern using boost pytho n lib

[Delaney, Timothy]

> The good news is that you do NOT need to wrap/expose non canonical
> objects.  A more reliable, flexible, sounder pattern is to wrap
> and expose "lightweight proxy" C++ objects -- that will internally
> delegate whatever is needed to your "one and only substantial
> object", but will NOT implement the singleton Design Pattern with
> the attendant efforts to ensure only one of them is ever subject
> to instantiation (whence the need to avoid copying, etc, etc, and
> hence the non-canonicality).
...
> Over the last week or so, the singleton DP came up for discussion
> a couple of times on this group -- I seem to be in a tiny minority
> in disliking it intensely in favour of featherweight proxies, though
> I know I'm NOT the only one since I recall a C++ Report article
> that made points very similar to mine.  www.google.com/groups should
> let you fetch and read the few relevant articles for background.

Just to add my support to Alex here - we haven't always agreed on everything
(c.f. ''.join() ;) but I'm in complete agreement in this case. Flyweight is
a *very* useful design pattern, whilst *public* Singleton is incredibly
difficult to enforce. You are best to have a private Singleton (i.e. it is
only visible to your code) and expose its interface via a Flyweight.
Simplest way to do this would be to have a non-static class only declared
and implemented and instantiated in the implementation (.cpp) file where
your Flyweight class is implemented. I think (been a while since I've done
any C++ work).

Tim Delaney