Re: newbie: question: i have a memory leak: obj-c 2.0: modification of program in "Cocoa with Objective-C"

FROM : Quincey Morris
DATE : Sun Feb 03 23:37:33 2008

On Feb 3, 2008, at 12:45, George Greene wrote:

> also, why was it necessary to use
> @property(copy, readwrite) NSString *name;
> @property(copy, readwrite) NSString *artist;
> instead of
> @property(readwrite) NSString *name;
> @property(readwrite) NSString *artist;


It isn't actually necessary. All you need to do to make the compiler 
warning go away is write:

@property(assign, readwrite) NSString *name;
@property(assign, readwrite) NSString *artist;

which is what the "(readwrite)" version means anyway.

What's at stake here is whether, if you pass a *mutable* string to 
setName or setArtist, it should keep a reference to the mutable string 
object in the instance variable, or whether it should keep a private 
copy of the string contents at that moment. Depending on the needs of 
your app, one or other might be the correct answer. The compiler is 
trying to warn you that the default of "assign" might not be what you 
wanted.

The problem is that the object's conformance to NSCopying is a lousy 
way to arbitrate the possible ambiguity. It's really got nothing to do 
with NSCopying at all. And the poor wording of the warning message 
isn't a help either.

I submitted a compiler bug for this a week or two ago, so we'll see if 
the compiler group listens to reason. ;)

P.S. In your case, "(copy, readwrite)" looks like the proper choice, 
but that's just a guess.