From: Dave Handley (dave_at_[hidden])
Date: 2005-01-07 12:59:02
Mikhail Glushenkov wrote:
> What about adapting Loki's Singleton? It's the best Singleton
> I know about and (probably) the most widely-known one.
I agree that it is probably one of the best ones around. My only issues
are:
1) Wouldn't it be better to use CRTP than the rather strange usage syntax
that Loki uses with a typedef and a requirement to make the
constructors/destructors private? It is remarkably easy if you are not
familiar with the Singleton implementation in Loki to make your
constructors/destructors public by mistake and then use them, whereas a CRTP
solution could make the base constructors/destructors protected.
2) There are probably some more options that need to be included, for
example making a Singleton be capable of destroying/recreating during the
run of a program. Consider a singleton that is managing a print queue. For
some reason all the printers go off-line, there is a potential for memory
optimisation by closing down the print queue. If printers come back on line
the print queue could come back on line - but that isn't possible (as far as
I know) with Loki.
3) What issues are there with the licensing of Loki?
David Greene wrote:
> I think that's a good place to start. What other patterns should
> we be looking at. We ought to start a wiki page.
>
> I would prefer to put the files in the sandbox so they are
> versioned, have history, etc. The yahoo files section is
> inconvenient due to the registration requirement.
I would be happy to submit what I have to the sandbox - who do I contact to
get on the sandbox as a developer, and is there a set of submission
guidelines? Where would the wiki page be? I also notice from a quick
browse of the sandbox that there is a set of classes for visitors, and that
they haven't really been touched for 2 years. Did these ever make it into
boost? Is there any documentation for them? And could we perhaps look
there for a starting point for the visitor side of things?
In my view, the best start for a list of patterns to look at is probably the
GoF book! I have written generic code in the past for:
1) Flyweights
2) Composites
3) Visitors
4) Singletons
5) Bridge (just to link the 2 classes easily)
There is certainly scope to include:
1) Factory Method
2) Abstract Factory
3) Decorator
4) Chain of responsibility
However, if we are to have a go at a project like this, I would suggest
keeping the initial submission list quite short, and then if there is some
interest further down track, follow on with more patterns.
Dave