Objective-C synthesize property name overriding

objective-c synthesizer
Thomas picture Thomas · Sep 27, 2010 · Viewed 15.4k times · Source

I am trying to understand the purpose of the synthesize directive with property name overriding. Say that I have an interface defined as follow:

@interface Dummy ... {
    UILabel *_dummyLabel;
}

@property (retain, nonatomic) UILabel *dummyLabel;

And in the implementation file, I have:

@synthesize dummyLabel = _dummyLabel;

From what i understand, "dummyLabel" is just an alias of the instance variable "_dummyLabel". Is there any difference between self._dummyLabel and self.dummyLabel?

Answer

Jacob Relkin picture Jacob Relkin · Sep 27, 2010

Yes. self._dummyLabel is undefined, however _dummyLabel is not.

Dot syntax expands out to simple method invocations, so it's not specific to properties. If you have a method called -(id)someObject, for example in the case of object.someObject, it will be as if you wrote [object someObject];.

self.dummyLabel  //works
self._dummyLabel //does not work
dummyLabel       //does not work
_dummyLabel      //works
[self dummyLabel];  //works
[self _dummyLabel]; //does not work

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