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
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--------------------------------------------
Stephen Milligan
Do you do the Badger?
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--------------------------------------------
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Do you do the Badger?
http://www.yellowbadger.com
Do you cfeclipse? http://www.cfeclipse.org
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