Question

I have a property that I do not synthesize, instead I create a getter and setter myself. Therefore, the ARC keywords (strong or weak) have no meaning, I assume, so I eliminate them. This works fine on Xcode 4.3, but when my coworker opens them on XCode 4.2 the compiler complains that there is no strong/weak keyword, so I instructed him to meaninglessly enter the keyword back in again. Which is correct (with or without keywords)?

To be clear: I have a property like this @property (nonatomic) NSString *foo and in the .m file I implement -(NSString *)foo and -(void)setFoo:(NSString *)foo and do NOT include @synthesize foo. Another relevant detail is that there is no corresponding iVar, instead the properties interact with a Core Data object. This will not compile in XCode 4.2 unless I add strong or weak to the keywords.

EDIT I thought of one more relevant thing, one of these properties is on a Protocol, I don’t know if that makes a difference.

Answer 1

The declared attributes that you are referencing are optional. To quote the documentation:

Property Declaration and Implementation
The @property directive declares a property. An optional parenthesized
set of attributes provides additional details about the storage
semantics and other behaviors of the property – see “Property Declaration Attributes” for possible values.

Property Declaration Attributes
You can decorate a property with
attributes by using the form @property(attribute [, attribute2, ...]).
Like methods, properties are scoped to their enclosing interface
declaration. For property declarations that use a comma-delimited list
of variable names, the property attributes apply to all of the named
properties.

If you use the @synthesize directive to tell the compiler to create
the accessor methods (see “Property Implementation Directives”), the
code it generates matches the specification given by the keywords. If
you implement the accessor methods yourself, you should ensure that it
matches the specification (for example, if you specify copy you must
make sure that you do copy the input value in the setter method).

If you then use @dynamic instead of @synthesize it is telling the compiler that you will be writing your own methods and prevents it from complaining when it doesn’t find suitable methods.

More information can be found here.