in reply to Re^9: what is a propper way to make a chunk of data accessible to all my packages for retrieval and modification ?
in thread what is a propper way to make a chunk of data accessible to all my packages for retrieval and modification ?

Well if you want to change your configuration depending upon the context, then of course you don't want a singleton... which is all about never changing (or overriding) anything wherever you are.

No it isn't. A singleton is about there only ever being one instance of a class. Nothing wrong with having a singleton instance whose state you can change.

Of course it's globals in disguise, but it's globals on steroids too, because you can share your globals across packages as needed :)

Of course you can share globals across packages.

{ package Foo;
  $foo = 1;
}
{ package Bar;
  print $Foo::foo, "\n";
}

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Re^11: what is a propper way to make a chunk of data accessible to all my packages for retrieval and modification ?
by wazoox (Prior) on Mar 08, 2006 at 12:38 UTC

    Well you're right I wasn't very clear :) You may of course change a singleton, but changes to it are obviously global to your app. If that's not what you want, then you don't want a singleton.

    Of course you can share globals across packages.

    Yeah sure, but in an OO-environment that means you're breaking encapsulation. Singletons don't.

[reply]
      You may of course change a singleton, but changes to it are obviously global to your app. If that's not what you want, then you don't want a singleton.

      But you might! The singleton class pattern isn't synonymous with static configuration. There are other uses for singletons.

      Yeah sure, but in an OO-environment that means you're breaking encapsulation. Singletons don't.

      Tell me how do singleton's break encapsulation any more/less than a set of package variables? If you're using them to return static configuration information (as you seem to be proposing) then they encapsulate exactly the same thing.

[reply]
        But you might! The singleton class pattern isn't synonymous with static configuration. There are other uses for singletons.

        I don't really mean singletons are only for configuration ! I just insist that singletons really are singletons; if you want a variation of a singleton locally in your program, that simply means you shouldn't be using a singleton in the first place.

        Tell me how do singleton's break encapsulation any more/less than a set of package variables? If you're using them to return static configuration information (as you seem to be proposing) then they encapsulate exactly the same thing.

        As I understand it accessing any variable inside another package directly is EVIL :) When using a singleton, you ask the object to provide you with the data (thru a getter/setter or whatever mecanism you're using, anything BUT direct access), you don't simply take it. That's the difference between breaking or not breaking encapsulation.

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