RE: [Flashcoders] Singleton in AS3
Have anyone got ideas how to implement Singleton pattern in AS3 best?
Constructor in AS3 can only be public or internal, which is not private
anyway. ..
Well, internal should be enough to implement a Singleton
Just have a public const in the package initialized with an internal class
of the package
Something like that
myTest/MySingleton.as
-
package myTest
{
public const MySingleton:Singleton = new Singleton();
}
-
myTest/Singleton.as
-
Package myTest
{
//default to internal, can only be accessed inside the package
class Singleton
{
//be sure to let the constructor internal
function Singleton()
{
//...
}
//be sure to have your methods/properties/etc. public
//so it can be accessed outside of the package
public function someMethod():String
{
//...
}
}
}
-
And after well
import myTest.MySingleton;
MySingleton.someMethod()
etc.
I don't see the need of a private constructors at all
And furthermore private constructors imho would cause
more problems than solutions
What people oversee is that we are in ECMAScript,
A Singleton in this context should just be an object
That you can not copy and/or inherit in another prototype
So a public read-only object.
Here having an internal class inside a package prevent
to instanciate this class outside of the package
the public const force to have only one global access point to the
instancied object
So where is the problem ?
Not having private constructors is not a bug,
It's using a private constructor to implement singleton
which is imho a bug/hack from AS2 times.
http://www.mozilla.org/js/language/es4/core/definitions.html
private - Makes the definition visible only in the enclosing class's private
namespace
so following the standard if you got a private constructor
you just CAN NOT instanciate at all the class anywhere else
than inside the class !
private constructors just does not make sens.
zwetan
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RE: [Flashcoders] Singleton in AS3
They do. With internal access modifier you're still able to create an instance of class directly. Not outside of the package, or if you have a code exemple That show that behaviour I would be interested to see it. zwetan ___ Flashcoders mailing list Flashcoders@chattyfig.figleaf.com http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
Re: [Flashcoders] Singleton in AS3
You can't yet as for the reason you stated. Bitch on the forums pretty please; you, many many others, and I all want this changed. http://www.macromedia.com/cfusion/webforums/forum/categories.cfm?catid=587entercat=y - Original Message - From: Michael Klishin [EMAIL PROTECTED] To: Flashcoders ML flashcoders@chattyfig.figleaf.com Sent: Thursday, November 10, 2005 12:16 PM Subject: [Flashcoders] Singleton in AS3 Hi guys, Have anyone got ideas how to implement Singleton pattern in AS3 best? Constructor in AS3 can only be public or internal, which is not private anyway. .. -- Michael Antares Klishin, Email: [EMAIL PROTECTED] Web: www.novemberain.com Non progredi est regredi ___ 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
RE: [Flashcoders] Singleton in AS3
Why should a public constructor prevent the creation of a Singleton? All you need is a static getInstance() method and a private attribute to hold the created instance. Sure, the public constructor means someone else could instantiate the class on their own without using getInstance(), but if you're writing the code, you'll do it the proper way anyhow, no? -Chris -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JesterXL Sent: Friday, November 11, 2005 1:32 PM To: Flashcoders mailing list Subject: Re: [Flashcoders] Singleton in AS3 You can't yet as for the reason you stated. Bitch on the forums pretty please; you, many many others, and I all want this changed. http://www.macromedia.com/cfusion/webforums/forum/categories.cfm?catid=587e ntercat=y - Original Message - From: Michael Klishin [EMAIL PROTECTED] To: Flashcoders ML flashcoders@chattyfig.figleaf.com Sent: Thursday, November 10, 2005 12:16 PM Subject: [Flashcoders] Singleton in AS3 Hi guys, Have anyone got ideas how to implement Singleton pattern in AS3 best? Constructor in AS3 can only be public or internal, which is not private anyway. .. -- Michael Antares Klishin, Email: [EMAIL PROTECTED] Web: www.novemberain.com Non progredi est regredi ___ 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
Re: [Flashcoders] Singleton in AS3
That's fine for use Flashers who are used to using such methods to get what we want. However, other languages are more strict, and from the perception of new programmers coming into ActionScript 3, not meeting their expectations is a failure of the language... to point. Bottom line, they see our methods as hacks, and that's a bad thing. The correct way is to use getInstance, yes. But, it should also throw an exception if you try to instantiate it: var a:MyClass = new MyClass(); That should not work, but it does currently because you have no choice. In an effort to make ActionScript more clean, strict, and helpful, this is one of the additions. The language itself should be self-explanatory to use it, and should support common programming patterns such as Singleton. Supporting design patterns in a language, to me is iffy, but there are a enough business use cases in my opinion to support it. - Original Message - From: Chris Wilson [EMAIL PROTECTED] To: 'Flashcoders mailing list' flashcoders@chattyfig.figleaf.com Sent: Friday, November 11, 2005 1:40 PM Subject: RE: [Flashcoders] Singleton in AS3 Why should a public constructor prevent the creation of a Singleton? All you need is a static getInstance() method and a private attribute to hold the created instance. Sure, the public constructor means someone else could instantiate the class on their own without using getInstance(), but if you're writing the code, you'll do it the proper way anyhow, no? -Chris -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JesterXL Sent: Friday, November 11, 2005 1:32 PM To: Flashcoders mailing list Subject: Re: [Flashcoders] Singleton in AS3 You can't yet as for the reason you stated. Bitch on the forums pretty please; you, many many others, and I all want this changed. http://www.macromedia.com/cfusion/webforums/forum/categories.cfm?catid=587e ntercat=y - Original Message - From: Michael Klishin [EMAIL PROTECTED] To: Flashcoders ML flashcoders@chattyfig.figleaf.com Sent: Thursday, November 10, 2005 12:16 PM Subject: [Flashcoders] Singleton in AS3 Hi guys, Have anyone got ideas how to implement Singleton pattern in AS3 best? Constructor in AS3 can only be public or internal, which is not private anyway. .. -- Michael Antares Klishin, Email: [EMAIL PROTECTED] Web: www.novemberain.com Non progredi est regredi ___ 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 ___ Flashcoders mailing list Flashcoders@chattyfig.figleaf.com http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
RE: [Flashcoders] Singleton in AS3
Agreed on all points, but when the deadline is approaching and the code needs to be done... Ironically to your points, I'm relatively new to Flash (~2 months), and have come to this language from C, C++, and Java. It's been *far* more difficult to learn than I expected, in many cases due to the hacks you mentioned. (Whaddya' mean 'this' doesn't refer to the class instance when you're in a callback function _that's_a_method_of_the_class_!?!) That said, I'm a pragmatist when it comes to finishing a project. :-] -Chris -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JesterXL Sent: Friday, November 11, 2005 1:51 PM To: Flashcoders mailing list Subject: Re: [Flashcoders] Singleton in AS3 That's fine for use Flashers who are used to using such methods to get what we want. However, other languages are more strict, and from the perception of new programmers coming into ActionScript 3, not meeting their expectations is a failure of the language... to point. Bottom line, they see our methods as hacks, and that's a bad thing. The correct way is to use getInstance, yes. But, it should also throw an exception if you try to instantiate it: var a:MyClass = new MyClass(); That should not work, but it does currently because you have no choice. In an effort to make ActionScript more clean, strict, and helpful, this is one of the additions. The language itself should be self-explanatory to use it, and should support common programming patterns such as Singleton. Supporting design patterns in a language, to me is iffy, but there are a enough business use cases in my opinion to support it. - Original Message - From: Chris Wilson [EMAIL PROTECTED] To: 'Flashcoders mailing list' flashcoders@chattyfig.figleaf.com Sent: Friday, November 11, 2005 1:40 PM Subject: RE: [Flashcoders] Singleton in AS3 Why should a public constructor prevent the creation of a Singleton? All you need is a static getInstance() method and a private attribute to hold the created instance. Sure, the public constructor means someone else could instantiate the class on their own without using getInstance(), but if you're writing the code, you'll do it the proper way anyhow, no? -Chris -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JesterXL Sent: Friday, November 11, 2005 1:32 PM To: Flashcoders mailing list Subject: Re: [Flashcoders] Singleton in AS3 You can't yet as for the reason you stated. Bitch on the forums pretty please; you, many many others, and I all want this changed. http://www.macromedia.com/cfusion/webforums/forum/categories.cfm?catid=587e ntercat=y - Original Message - From: Michael Klishin [EMAIL PROTECTED] To: Flashcoders ML flashcoders@chattyfig.figleaf.com Sent: Thursday, November 10, 2005 12:16 PM Subject: [Flashcoders] Singleton in AS3 Hi guys, Have anyone got ideas how to implement Singleton pattern in AS3 best? Constructor in AS3 can only be public or internal, which is not private anyway. .. -- Michael Antares Klishin, Email: [EMAIL PROTECTED] Web: www.novemberain.com Non progredi est regredi ___ 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 ___ 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
Re: [Flashcoders] Singleton in AS3
I totally agree bro... but ActionScript is moving away from a pure RAD type of language, hence being more strict. Exactly; hopefully people from your background won't have pain in the future. Again, as it's been funnily pointed out, Ruby and Java both have been trying to get more dynamic why we get more strict, but bottom line, both started from different points and have different business goals. - Original Message - From: Chris Wilson [EMAIL PROTECTED] To: 'Flashcoders mailing list' flashcoders@chattyfig.figleaf.com Sent: Friday, November 11, 2005 1:59 PM Subject: RE: [Flashcoders] Singleton in AS3 Agreed on all points, but when the deadline is approaching and the code needs to be done... Ironically to your points, I'm relatively new to Flash (~2 months), and have come to this language from C, C++, and Java. It's been *far* more difficult to learn than I expected, in many cases due to the hacks you mentioned. (Whaddya' mean 'this' doesn't refer to the class instance when you're in a callback function _that's_a_method_of_the_class_!?!) That said, I'm a pragmatist when it comes to finishing a project. :-] -Chris -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JesterXL Sent: Friday, November 11, 2005 1:51 PM To: Flashcoders mailing list Subject: Re: [Flashcoders] Singleton in AS3 That's fine for use Flashers who are used to using such methods to get what we want. However, other languages are more strict, and from the perception of new programmers coming into ActionScript 3, not meeting their expectations is a failure of the language... to point. Bottom line, they see our methods as hacks, and that's a bad thing. The correct way is to use getInstance, yes. But, it should also throw an exception if you try to instantiate it: var a:MyClass = new MyClass(); That should not work, but it does currently because you have no choice. In an effort to make ActionScript more clean, strict, and helpful, this is one of the additions. The language itself should be self-explanatory to use it, and should support common programming patterns such as Singleton. Supporting design patterns in a language, to me is iffy, but there are a enough business use cases in my opinion to support it. - Original Message - From: Chris Wilson [EMAIL PROTECTED] To: 'Flashcoders mailing list' flashcoders@chattyfig.figleaf.com Sent: Friday, November 11, 2005 1:40 PM Subject: RE: [Flashcoders] Singleton in AS3 Why should a public constructor prevent the creation of a Singleton? All you need is a static getInstance() method and a private attribute to hold the created instance. Sure, the public constructor means someone else could instantiate the class on their own without using getInstance(), but if you're writing the code, you'll do it the proper way anyhow, no? -Chris -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JesterXL Sent: Friday, November 11, 2005 1:32 PM To: Flashcoders mailing list Subject: Re: [Flashcoders] Singleton in AS3 You can't yet as for the reason you stated. Bitch on the forums pretty please; you, many many others, and I all want this changed. http://www.macromedia.com/cfusion/webforums/forum/categories.cfm?catid=587e ntercat=y - Original Message - From: Michael Klishin [EMAIL PROTECTED] To: Flashcoders ML flashcoders@chattyfig.figleaf.com Sent: Thursday, November 10, 2005 12:16 PM Subject: [Flashcoders] Singleton in AS3 Hi guys, Have anyone got ideas how to implement Singleton pattern in AS3 best? Constructor in AS3 can only be public or internal, which is not private anyway. .. -- Michael Antares Klishin, Email: [EMAIL PROTECTED] Web: www.novemberain.com Non progredi est regredi ___ 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 ___ 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
Re: [Flashcoders] Singleton in AS3
Chris Wilson wrote: Agreed on all points, but when the deadline is approaching and the code needs to be done... That said, I'm a pragmatist when it comes to finishing a project. :-] For sure. But as long as AS3 is going to become one of senior programming languages... ;) -- Michael Antares Klishin, Email: [EMAIL PROTECTED] Web: www.novemberain.com Non progredi est regredi ___ Flashcoders mailing list Flashcoders@chattyfig.figleaf.com http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
Re: [Flashcoders] Singleton in AS3
Have anyone got ideas how to implement Singleton pattern in AS3 best?
Constructor in AS3 can only be public or internal, which is not private
anyway
Hey Michael,
One way (as mentioned in another email) is to throw an error in the
constructor if some restriction has not been met. The following example may
not be the *greatest* hack, because there really isn't any way to catch the
error that's being thrown. But it's a hack that gets you to a singleton with
pretty high confidence that it was created via the factory method. Another
(more complicated) alternative is to use some convoluted namespace scheme.
Another (less reliable) possibility is to simply pass an argument to the
constructor - and throw if the argument is null.
I have to admit that I've been one of the most vocal proponents for the
private constructor argument, but want to make the point that the Singleton
pattern should be avoided whenever possible. It's very difficult to isolate
and test singletons, you wind up needing to add a destroy method or some
such other hack.
In my experience, almost every time I find myself leaning toward a
Singleton, I find a more elegant OO solution.
Here's a pretty good discussion about why to avoid Singletons:
http://www.softwarereality.com/design/singleton.jsp
I hope this helps.
Luke Bayes
www.asunit.org http://www.asunit.org
package {
import flash.util.trace;
import flash.errors.IllegalOperationError;
import flash.util.setTimeout;
public class SingletonExample {
private static var instance:SingletonExample;
public function SingletonExample(isSingleton:Boolean = false) {
setTimeout(checkSingleton, 1);
}
private function checkSingleton():Void {
if(this != SingletonExample.instance) {
throw new IllegalOperationError(SingletonExample instantiated directly, you
should use the static getInstance method instead);
}
}
public static function getInstance():SingletonExample {
if(SingletonExample.instance == null) {
SingletonExample.instance = new SingletonExample(true);
}
return SingletonExample.instance;
}
public function toString():String {
return Singleton instance created successfully;
}
}
}
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Re: [Flashcoders] Singleton in AS3
Security by obscurity, while applicable satisfying pioneers early adopters, is still unacceptable; we need private constructors. However, you do bring up a good point; I think, non intentionally, the new mx framework works like that; like, they use namespaces, in part to support namespaces for MXML (I think). - Original Message - From: Fruber Malcome [EMAIL PROTECTED] To: 'Flashcoders mailing list' flashcoders@chattyfig.figleaf.com Sent: Friday, November 11, 2005 10:24 PM Subject: RE: [Flashcoders] Singleton in AS3 There are many cases where you'd want to ensure that someone can't create a new instance of a class that you've published. An interesting workaround is to hide your class in a namespace that is 'not publicly known', then write a wrapper class that someone can call NEW on - and the constructor of that class checks to see if that object exists. This doesn't ensure that it doesn't happen, but someone would have to have intimate knowledge of some unknown namespace in order to create an instance of that object.. Just an idea. Thanks - Fruber -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Chris Wilson Sent: Friday, November 11, 2005 10:40 AM To: 'Flashcoders mailing list' Subject: RE: [Flashcoders] Singleton in AS3 Why should a public constructor prevent the creation of a Singleton? All you need is a static getInstance() method and a private attribute to hold the created instance. Sure, the public constructor means someone else could instantiate the class on their own without using getInstance(), but if you're writing the code, you'll do it the proper way anyhow, no? -Chris -Original Message- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of JesterXL Sent: Friday, November 11, 2005 1:32 PM To: Flashcoders mailing list Subject: Re: [Flashcoders] Singleton in AS3 You can't yet as for the reason you stated. Bitch on the forums pretty please; you, many many others, and I all want this changed. http://www.macromedia.com/cfusion/webforums/forum/categories.cfm?catid=587e ntercat=y - Original Message - From: Michael Klishin [EMAIL PROTECTED] To: Flashcoders ML flashcoders@chattyfig.figleaf.com Sent: Thursday, November 10, 2005 12:16 PM Subject: [Flashcoders] Singleton in AS3 Hi guys, Have anyone got ideas how to implement Singleton pattern in AS3 best? Constructor in AS3 can only be public or internal, which is not private anyway. .. -- Michael Antares Klishin, Email: [EMAIL PROTECTED] Web: www.novemberain.com Non progredi est regredi ___ 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 ___ 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
