@property definitions with ARC: strong or retain?

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To answer all three questions in one: retain and strong are synonymous with each other, so both are correct. The documentation states

retain implies __strong ownership

strong implies __strong ownership

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1) Shouldn't retain now be replace with strong or weak?

No. You cannot replace retain with weak; they are different. And strong is a 100% synonym for retain; they are identical. You can use either, so there is no "should" here. You can replace retain with strong if you like, but you don't have to.

2) Why does the auto-generated code still use retain

Why not? See (1). retain is correct so there is no problem.

3) What is the correct replacement for retain in this property statement?

There is no need to replace retain.

I'm currently debugging a problem using NSFetchRequest, and I thought this might be the source of the problem. Thoughts?

It isn't.

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Before ARC, you have to 'release' an object which is retained. That mean retain has counter part. After ARC you don't need to release. So use strong. Its a visual clue that you don't need to call release.

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"retain" is equals to "strong".

"strong" is used for example:

@property (nonatomic, strong) NSString * someString;

And "__strong" is used for example:

-(void) someMethod
{
__strong NSString* vStr = [[NSString alloc] initWithString:@"some string"];
}

On Apple Docs. says:

Property Attributes

The keywords weak and strong are introduced as new declared property attributes, as shown in the following examples.

// The following declaration is a synonym for: @property(retain) MyClass *myObject;
property(strong) MyClass *myObject;

Apple doc. http://developer.apple.com/library/ios/#releasenotes/ObjectiveC/RN-TransitioningToARC/Introduction/Introduction.html