Sure,
Here's a slightly more complete implementation of that last example:
public class CurrencyFormatter {
private static formatter:CurrencyFormatter;
public function getInstance():CurrencyFormatter {
// use ExternalInterface or IP lookup or whatever to determine locale
if (locale == "UK") {
formatter = new UKCurrencyFormatter();
} else {
formatter = new USCurrencyFormatter();
}
return formatter;
}
class USCurrencyFormatter extends CurrencyFormatter {
public formatValue(val:Number) {
// very simplistic formatting
return "$" + String(val);
}
}
class UKCurrencyFormatter extends CurrencyFormatter {
public formatValue(val:Number) {
// very simplistic formatting
return "£" + String(val);
}
}
}
Let me know if that explains it a bit better.
Spike
On 10/29/05, JesterXL <[EMAIL PROTECTED]> wrote:
>
> Can you elaborate? Why wouldn't the static class work in that case?
>
> ----- Original Message -----
> From: "Spike" <[EMAIL PROTECTED]>
> To: "Flashcoders mailing list" <flashcoders@chattyfig.figleaf.com>
> Sent: Friday, October 28, 2005 9:54 PM
> Subject: Re: [Flashcoders] Newbie AS3 question
>
>
> ok,
>
> That's just a static class.
>
> Like I said, there's a subtle but important difference between singleton
> and
> a static class.
>
> Here's another example.
>
> You have a requirement to provide a currency formatter.
>
> One way to do this is to create a singleton that returns a different
> currency formatter depending on which locale you are in.
>
> So in the class you would have something like this (Omitting method
> declarations for simplicty):
>
> public class CurrencyFormatter {
>
> class USCurrencyFormatter extends CurrencyFormatter {
>
> }
>
>
> class UKCurrencyFormatter extends CurrencyFormatter {
>
> }
> }
>
> Now if I call CurrencyFormatter.getInstance() it gives me the correct
> formatter for my locale.
>
> With your static class approach you have to check in every method what the
> locale is and handle it accordingly. That's fine for one or two locales,
> but
> if you want to handle 20, it gets pretty ugly.
>
> You can solve the problem in other ways of course, but it does demonstrate
> the difference between static classes and the singleton pattern. The
> singleton pattern offers you a lot more possibilities.
>
> Spike
>
> On 10/29/05, JesterXL <[EMAIL PROTECTED]> wrote:
> >
> > To clarify:
> >
> >
> > class ServerConnection
> > {
> > private static var url;
> > private static var port;
> > private static var socket;
> >
> > public static function connect(p_url, p_port)
> > {
> > url = p_url;
> > port = p_port;
> > socket = new Socket();
> > socket.connect(url, port);
> > }
> >
> > public static function getData()
> > {
> > // Simple function that gets something from the server.
> > }
> > }
> >
> > Then to use:
> >
> > ServerConnection.connect(myURL, myPort);
> >
> > ----- Original Message -----
> > From: "JesterXL" <[EMAIL PROTECTED]>
> > To: "Flashcoders mailing list" <flashcoders@chattyfig.figleaf.com>
> > Sent: Friday, October 28, 2005 9:25 PM
> > Subject: Re: [Flashcoders] Newbie AS3 question
> >
> >
> > Naw, I don't know the exact way Singleton is implemented, hence my long
> > battle with finding clarification. It could of been solved in 10 seconds
> > over a beer, but email sux.
> >
> > I figured Math.abs was the Singleton pattern, and ARP, me, Sho, Steven
> > Webster, and everyone else apparently has their own version of
> Controller
> > as
> > well. I figured I knew enough to use it.
> >
> > For instance, your example makes perfect sense and I can see why you'd
> > want
> > to do it that way. I, on the other hand would just put an if then
> > statement
> > in the connect method or whatever to ensure we're connected before
> making
> > a
> > method call, else throw an exception.
> >
> > Are they both the Singleton pattern? Does it matter?
> >
> >
> > ----- Original Message -----
> > From: "Spike" <[EMAIL PROTECTED]>
> > To: "Flashcoders mailing list" <flashcoders@chattyfig.figleaf.com>
> > Sent: Friday, October 28, 2005 7:14 PM
> > Subject: Re: [Flashcoders] Newbie AS3 question
> >
> >
> > Hmmm....
> >
> > >From your explanation, I think either I don't understand what happens
> in
> > >AS,
> > or you're misunderstanding the use of the singleton pattern.
> >
> > In an attempt to understand better, here's an example of where I would
> use
> > the singleton pattern.
> >
> > I have a requirement to talk to a socket on a server, but I need to make
> > sure that I only ever have a single connection from each user.
> >
> > So...
> >
> > I create a ServerConnection class that has something like this (ignoring
> > private constructors etc.):
> >
> > ServerConnection {
> >
> > private static instance:ServerConnection;
> >
> > static function getInstance() {
> > if (this.instance == null) {
> > instance = new ServerConnection(url,port);
> > } else {
> > // make sure that the port and url for the instance match the passed url
> > and
> > port.
> > // if not, barf an error
> > }
> > return instance;
> > }
> >
> > public function getData() {
> > // Simple function that gets something from the server.
> > }
> > }
> >
> > ok, so I have now guaranteed that I will only ever create a single
> > connection to the server because I'm always getting the same object back
> > regardless of how many times I call getInstance() in my code.
> >
> > So I can happily do this anywhere I like in my code:
> >
> > ServerConnection.getInstance().getData()
> >
> > If I had something like what you have in the Math class, the getData()
> > method would have to be declared as static and it would have to check
> > every
> > time you called it to see if there was an active connnection to the
> > server.
> > If not it would have to create one and you would have to hope that 2
> > method
> > calls didn't step on each other and create multiple server connections.
> >
> > Not sure if that clarifies or confuses, but hopefully you can let me
> know
> > if
> > and how it differs in Flash.
> >
> > Spike
> >
> > On 10/28/05, JesterXL <[EMAIL PROTECTED]> wrote:
> > >
> > > ActionScript 2, no, no difference. You actually have to do a tincy bit
> > of
> > > extra work to get AS2 to support getInstance like I've seen it in
> Java.
> > >
> > > This all goes way in AS3 since prototype is strictly in the hands of
> > > flash.util.Proxy; basically, prototype is now read-only, and Proxy is
> > the
> > > only one who can wriggle around the rules in the new AVM.
> > >
> > > That's the one thing that always pissed me off about Cairngorm, and I
> > > debated for days on the ARP Advisory list till I was overulled merely
> by
> > > strength of numbers of opposing viewpoints.
> > >
> > > First, to clarify, when I speak of Singleton.getInstance(), I speak of
> > the
> > > only way to utilize the Singleton's methods, so yes, if you want to
> call
> > > it
> > > calling a method on an instance, that's fine, but it's still spoken of
> > as
> > > a
> > > Singleton only has 1 instance.
> > >
> > > That being the case, what I used to like to do was, even from AS1:
> > >
> > > class MyClass
> > > {
> > > public static function sup()
> > > {
> > > trace("yo");
> > > }
> > > }
> > >
> > > Which boils down to:
> > >
> > > function MyClass()
> > > {
> > > }
> > >
> > > MyClass.sup = function()
> > > {
> > > trace("yo");
> > > };
> > >
> > > Therefore, allowing this:
> > >
> > > MyClass.sup();
> > >
> > > Since Functions are objects in ActionScript 1 & 2, and about the same
> in
> > > 3.
> > >
> > > However, when talking about why EventDispatcher in Cairngorm, and
> > > Controller
> > > in ARP both have the getInstance method, I was told that it was to
> > ensure
> > > that there was only ever 1 instance of it.
> > >
> > > I replied that there is; it's already defined, use it. Math.abs()
> works
> > > just fine, you don't do Math.getInstance().abs(), so why should I have
> > to
> > > do
> > > that extra function when I know there is only 1 instance, and it's
> > static,
> > > and ready to go?
> > >
> > > Fast-forward 4 days, class based vs. protoytpe languages, and
> > demographics
> > > exploration later, and I see their point; if you don't understand how
> > > ActionScript is written, doing things like Math.random() really
> doesn't
> > > make
> > > any sense to traditional programmers, and having to know that much
> about
> > > how
> > > a language works is really unfair, doesn't make people want to dive in
> > > without it being familiar & comfortable, and is an elitist stance.
> > >
> > > So, although I think getIstance() isn't technically needed (in AS1 or
> > > AS2),
> > > I still see the need for it, and respect it from a traditional
> developer
> > > standpoint.
> > >
> > > ----- Original Message -----
> > > From: "Spike" <[EMAIL PROTECTED]>
> > > To: "Flashcoders mailing list" <flashcoders@chattyfig.figleaf.com>
> > > Sent: Friday, October 28, 2005 6:38 PM
> > > Subject: Re: [Flashcoders] Newbie AS3 question
> > >
> > >
> > > *snip*
> > > AS3 and Flex both hammer the point that this really has little use
> other
> > > than confirming for those programmers who are not familiar with
> > > ActionScript. Same goes for the Singleton.method vs.
> > > Singleton.getInstance().method argument; the latter is for those
> > > programmers
> > > who don't know ActionScript well.
> > > *snip*
> > >
> > > Maybe there's something I don't understand, or maybe you typed it
> wrong,
> > > but
> > > in every other OO language I've dealt with there's a significant but
> > > subtle
> > > difference between
> > >
> > > Singleton.getInstance().method()
> > >
> > > and
> > >
> > > Singleton.method()
> > >
> > > The former is calling an instance method and the latter is calling a
> > > static
> > > method.
> > >
> > > Instance methods have access to instance data that is persisted as
> long
> > as
> > > the instance exists, static methods have access only to static data
> and
> > > that
> > > data passed in to the method call.
> > >
> > > Is this not true in ActionScript?
> > >
> > > Spike
> > >
> > > On 10/28/05, JesterXL <[EMAIL PROTECTED]> wrote:
> > > >
> > > > I'm the opposite end of the spectrum. This:
> > > >
> > > > class Box extends UIObject
> > > > {
> > > > function doStuff()
> > > > {
> > > > move(x + 10, y + 10);
> > > > setSize(width + 100, height + 100);
> > > > visible = !visible;
> > > > }
> > > > }
> > > >
> > > > looks more readable to me than:
> > > >
> > > > class Box extends UIObject
> > > > {
> > > > function doStuff()
> > > > {
> > > > this.move(this.x + 10, this.y + 10);
> > > > this.setSize(this.width + 100, this.height + 100);
> > > > this.visible = !this.visible;
> > > > }
> > > > }
> > > >
> > > > To each their own. I can see it justified in extending intrinsic
> > > classes,
> > > > as the first parameter to setInterval, and the first parameter in
> > > > Delegate.
> > > >
> > > > AS3 and Flex both hammer the point that this really has little use
> > other
> > > > than confirming for those programmers who are not familiar with
> > > > ActionScript. Same goes for the Singleton.method vs.
> > > > Singleton.getInstance().method argument; the latter is for those
> > > > programmers
> > > > who don't know ActionScript well.
> > > >
> > > > If you do it every day, there is no point.
> > > >
> > > > ----- Original Message -----
> > > > From: "Muzak" <[EMAIL PROTECTED]>
> > > > To: "Flashcoders mailing list" <flashcoders@chattyfig.figleaf.com>
> > > > Sent: Friday, October 28, 2005 5:37 PM
> > > > Subject: Re: [Flashcoders] Newbie AS3 question
> > > >
> > > >
> > > > Well, to me it's the other way around.
> > > > Code that doesn't use proper references looks messy to me.
> > > >
> > > > Whe I'm lazy or in a hurry, I do skip them, but I usually find
> myself
> > > > adding
> > > > them afterwards anyway.
> > > >
> > > > So, I'm with ryanm on this one ;-)
> > > >
> > > > regards,
> > > > Muzak
> > > >
> > > > ----- Original Message -----
> > > > From: "Martin Wood" <[EMAIL PROTECTED]>
> > > > To: "Flashcoders mailing list" <flashcoders@chattyfig.figleaf.com>
> > > > Sent: Friday, October 28, 2005 11:03 PM
> > > > Subject: Re: [Flashcoders] Newbie AS3 question
> > > >
> > > >
> > > > >
> > > > >
> > > > > ryanm wrote:
> > > > >>> What I don't get is why it needs "this.addChild" instead of just
> > > > >>> addChild. I've been sick of the keyword "this" for a long time
> > > > >>> and have since avoided it in AS2.
> > > > >>>
> > > > >>> Any reason that it needs to be back in for AS3?
> > > > >>>
> > > > >> Maybe because it's one of the most useful scope references ever
> > > > >> invented?
> > > > >>
> > > > >> The fundamental concept that you seem to miss is that "addChild"
> is
> > > > >> meaningless by itself, it is a method of an object (in
> > > > >> proper OOP development), and if you just say "addChild", who is
> > > adding
> > > > >> the child?
> > > > >
> > > > > the context is the current class. Occasionally 'this' is useful if
> > you
> > > > > happen to name a method parameter or local variable the
> > > > > same as a member variable and need to distinguish the two.
> > > > >
> > > > > But, I dont agree that its bad form to leave it out, nor is it any
> > > more
> > > > > difficult to maintain.
> > > > >
> > > > > in my opinion putting 'this' in everywhere to me just makes things
> > > > harder
> > > > > to read.
> > > > >
> > > > > thanks,
> > > > >
> > > > > Martin
> > > >
> > > >
> > > > _______________________________________________
> > > > Flashcoders mailing list
> > > > Flashcoders@chattyfig.figleaf.com
> > > > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
> > > >
> > > > _______________________________________________
> > > > Flashcoders mailing list
> > > > Flashcoders@chattyfig.figleaf.com
> > > > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
> > > >
> > >
> > >
> > >
> > > --
> > > --------------------------------------------
> > > Stephen Milligan
> > > Do you do the Badger?
> > > http://www.yellowbadger.com
> > >
> > > Do you cfeclipse? http://www.cfeclipse.org
> > > _______________________________________________
> > > Flashcoders mailing list
> > > Flashcoders@chattyfig.figleaf.com
> > > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
> > >
> > > _______________________________________________
> > > Flashcoders mailing list
> > > Flashcoders@chattyfig.figleaf.com
> > > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
> > >
> >
> >
> >
> > --
> > --------------------------------------------
> > Stephen Milligan
> > Do you do the Badger?
> > http://www.yellowbadger.com
> >
> > Do you cfeclipse? http://www.cfeclipse.org
> > _______________________________________________
> > Flashcoders mailing list
> > Flashcoders@chattyfig.figleaf.com
> > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
> >
> > _______________________________________________
> > Flashcoders mailing list
> > Flashcoders@chattyfig.figleaf.com
> > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
> >
> > _______________________________________________
> > Flashcoders mailing list
> > Flashcoders@chattyfig.figleaf.com
> > http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
> >
>
>
>
> --
> --------------------------------------------
> Stephen Milligan
> Do you do the Badger?
> http://www.yellowbadger.com
>
> Do you cfeclipse? http://www.cfeclipse.org
> _______________________________________________
> Flashcoders mailing list
> Flashcoders@chattyfig.figleaf.com
> http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
>
> _______________________________________________
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> http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
>
--
--------------------------------------------
Stephen Milligan
Do you do the Badger?
http://www.yellowbadger.com
Do you cfeclipse? http://www.cfeclipse.org
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