GCC 4.2 warning for object that no longer exsists

I had an NSString named responseReference that I put in a @property like so...

@property (nonatomic) NSString *responseReference;

and I got the warning:

No 'assign', 'retain', or 'copy' attribute is specified - 'assign' is assumed
Assign attribute (default) not appropriate for non-gc object property 'responseReference'

So to simply fix it I changed the code to this:

@property (nonatomic, retain) NSString *responseReference;

but I still got the开发者_开发技巧 warnings. I tried many things and ended up trying to remove the warnings by just removing the object from existence. But even when responseReference was no longer a part of ANY of my code it still gave me the exact same warning for responseReference. So I restarted X-Code. No beans.

Can anyone explain why it's giving me these warnings even though the object it's talking about doesn't exist? Also, do these warnings mean that my compiled code is affected?