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From: Daniel T. on 1 Nov 2007 22:00
Peter Duniho <NpOeStPeAdM(a)NnOwSlPiAnMk.com> wrote:
> "Daniel T." <daniel_t(a)earthlink.net> said:
>
> > The whole point of a singleton is to "Ensure a class only has one
> > instance, <i>and provide a global point of access to it.</i>" (GoF pg.
> > 127 emphasis added.) Global access, means global IMO.
>
> I understand that "singleton" has a perhaps a very specific meaning in
> the particular book in which (it seems) this whole idea of "design
> patterns" was first suggested.
>
> However, I see nothing to prevent someone from implementing a singleton
> that is not accessible globally. And I would still call it a singleton.
>
> Furthermore, in C# any singleton itself is not accessible globally; you
> need to start with the namespace, and then a particular class name, at
> a minimum.
>
> I don't see the point in raising the question of whether globals can
> exist in C# anyway, but assuming the question has been raised it seems
> silly to insist that the singleton pattern is somehow related to the
> question. You have to define "global" first before you can say whether
> the singleton pattern exists if and only if globals do, and once you've
> defined "global", you don't need to look at the singleton pattern to
> decide whether they exist in a language or not.

Fine, ignore the reference to globals. The question to the OP still
stands. I'm trying to help the OP solve his problem. In order to do so,
I would like to know how he would have solved it if he had known of the
design up front instead of it being a design change.
From: AndyW on 15 Nov 2007 02:32
On Wed, 31 Oct 2007 19:30:23 -0000, Bilz <BrianGenisio(a)gmail.com>
wrote:

>Hello,
>
>I am looking for a good pattern. I have a rather large software app
>that makes use of a service manager for its many services...
>configuration, colors, data lookup, units, etc. Up until now the
>service manager has been a singleton and anyone who wants access to a
>service just asks the singleton.
>
>Now we have a new requirement... run multiple instances of the
>software in the same application space with different configurations.
><sarcasm>shocking</sarcasm>
>
>So, now I need to think about a good design pattern to help me here.
>I can only come up with two awkward options:
>
>1. Pass a service manager key to every constructor of every class that
>needs access to the service manager. The class can go to a singleton
>to ask for the instance of the service manager by key. This is
>awkward and I don't like it.
>
>2. Create an interface for getting a service, and have every object in
>the object tree implement the interface. Pass a "parent" object
>reference to the "child" and implement the interfaces so they climb
>the tree all the way to the root node to get an instance of the
>service manager stored in the root node. This is better, but still
>awkward.
>
>Is there a better design pattern out there to do what I need? I am
>using .NET C#, though it shouldn't matter too much (unless .NET
>already has a service I can leverage).
>
>Thanks,
>Brian


Sounds like you just need to implement versioning in a WCF
application.
----------------
AndyW,
Mercenary Software Developer
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