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Re: Sorting an NSDictionary?
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Re: Sorting an NSDictionary?

  • Subject: Re: Sorting an NSDictionary?
  • From: "Michael B. Johnson" <email@hidden>
  • Date: Mon, 14 Jan 2002 22:55:47 -0800
On Monday, January 14, 2002, at 10:14 PM, cocoa-dev-
email@hidden wrote:

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Today's Topics:

1. Re: Sorting an NSDictionary? (Erik M. Buck)
2. Sub-pixel text placement (Dustin Mierau)
3. Re: NSWorkspaceDidTerminateApplicationNotification bug? (Mike Davis)
4. Re: Drawing an image in a CustomView (Erik M. Buck)
5. Re: NSWorkspaceDidTerminateApplicationNotification bug? (Bill Bumgarner)

--__--__--

Message: 1
From: "Erik M. Buck" <email@hidden>
To: "Jeff Galyan" <email@hidden>, "Cocoa-Dev List"
<email@hidden>
Subject: Re: Sorting an NSDictionary?
Date: Mon, 14 Jan 2002 22:12:48 -0600
Organization: EMB & Assocites Inc.

As the NSDictionary and NSMapTable and other documentation will tell you,
all objects stored must implement the informal protocol that includes the
methods -compare: and -hash. Since NSObject already implements these
methods, you are in good shape unless you want to customize the behavior.
If you do implement -compare: or -hash, remember that any two objects that
have the same hash must also compare as equal or bad things will happen.

Another UNDOCUMENTED as far as I know issue is that dictionary keys are
COPIED and therefore objects used as keys must conform to the NSCopying
(sp?) protocol.


This bit me as well when I first start using dictionaries, but it's quite well documented, once you look - in NSDictionary, I see:

Each value object receives a retain message before being added to the dictionary. In contrast, each key is copied (using copyWithZone:; keys must conform to the NSCopying protocol), and the copy is added to the dictionary.


--> Michael B. Johnson, Ph.D. -- email@hidden
--> Studio Tools, Pixar Animation Studios
--> http://xenia.media.mit.edu/~wave

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