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Re: Potential trick for adding instance variables to classes using poseAs

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Re: Potential trick for adding instance variables to classes using poseAs

Subject: Re: Potential trick for adding instance variables to classes using poseAs
From: Glenn Andreas <email@hidden>
Date: Fri, 19 Nov 2004 09:51:28 -0600

At 12:44 AM +1100 11/20/04, Wade Tregaskis wrote:

Forward Disclaimer: this is all nasty business. No whinging. :P

Very nasty, actually, since it sounds like you were trying to replace a class with another class that wasn't a subclass of the original class (because if it were, it would have already had the correct size). That is probably worse mojo than changing the size of ivars.

And more than just increasing the size, you can add in your items by name as you would normally, and access them like normal. Fantastic! :)

At least, it seems so, so far... I'm thinking this might give some real headaches if a subclass of the class you're posing as defines it's own instance variables too... ick. Still, it seems like it could work in very controlled cases. I thought I'd share this for objective criticism and general interest. No flaming, please - refer to the disclaimer. :)

Note that it is nearly impossible to know for sure that a given class doesn't have a subclass (which could have it's own instance vars), especially if that app supports loadable bundles (such as plugins) - and if you're adding your code to an app this pretty much means that somebody else can as well. Even if it doesn't you can't tell - examining the binary to discover all possible classes isn't even a guarentee, since classes can be generated at runtime (for example, if it uses a scripting language with an Objective-C bridge such as Python + PyObjC, or even in other cases).

If you want to add extra ivars to an existing class, search the archives on this topic - various techniques to emulate this have already been given...

It is pretty amazing how much you can abuse the runtime, though. Dynamically generating new classes, dynamically patching specific methods at runtime, all sorts of fun stuff... (just look at bindings as an example).

-- Glenn Andreas email@hidden <http://www.gandreas.com/> oh my! Mad, Bad, and Dangerous to Know _______________________________________________ Do not post admin requests to the list. They will be ignored. Cocoa-dev mailing list (email@hidden) Help/Unsubscribe/Update your Subscription: This email sent to email@hidden References: >Potential trick for adding instance variables to classes using poseAs (From: Wade Tregaskis <email@hidden>) Prev by Date: Re: Fastest way to push strings to the screen in an NSView? Next by Date: User click lost in space for a NSTableView Previous by thread: Potential trick for adding instance variables to classes using poseAs Next by thread: Re: Cocoa-dev Digest, Vol 1, Issue 303 Index(es): Date Thread