Extending Python with C++ singleton pattern using boost python lib

[Alex Martelli]

"Delaney, Timothy" <tdelaney at avaya.com> wrote in message
news:mailman.988071155.16112.python-list at python.org...
    [snip]
> > 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
    ...
> 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

Ok, not QUITE so tiny:-).

> 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.

...and then there is no need for the Singleton Design Pattern -- just
instance the 'whatever' only once, it IS your code so that ain't hard:-).

> 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).

Yep, that would work.  Or you may 'risklessly' expose it by putting it
as a private nested class inside your public flyweight class, with
its sole instance as a private static member for the flyweight class
(I think your idea works better though).


Alex