assign NSMutableArray with @property and 'copy' attribute
ios, objective-c
Solution
In Objective-C, the `copy` attribute in a property means the setter synthesized will look like this:
-(void)setMasterBirdSightingList:(NSMutableArray*)newValue
{
if (_masterBirdSightingList == newValue) return;
// NSMutableArray* oldValue = _masterBirdSightingList;
_masterBirdSightingList = [newValue copy];
// [oldValue release]; // <-- not applicable in ARC.
}
and that dot syntax will always be translated to
[self setMasterBirdSightingList:sightingList];
regardless of the attribute of the property.
The "allocated for another space to preserve stuffs from sightingList" stuff is done via the `-copy` method. The way you pass the argument to the setter's `newValue` parameter is irrelevant.
Edit: As @David mentioned in the comment, the `-copy` method of a mutable type returns an immutable object. You have to override the setter to call `-mutableCopy` instead. See What's the best way to use Obj-C 2.0 Properties with mutable objects, such as NSMutableArray?.
Problem
I'm following an official tutorial Your second iOS App:Storyboard and it told me to declare a property masterBirdSightingList like this(just a specific example and not necessary to know the context) : ``` @property (nonatomic, copy) NSMutableArray *masterBirdSightingList; ``` Note that there's an attribute copy. and then synthesize this property : ``` @synthesize masterBirdSightingList = _masterBirdSightingList; ``` And next there's one init method which made me confused : ``` - (void)initializeDefaultDataList { NSMutableArray *sightingList = [[NSMutableArray alloc] init]; self.masterBirdSightingList = sightingList; [self addBirdSightingWithName:@"Pigeon" location:@"Everywhere"]; } ``` Definitely sightingList is allocated for spaces and then it's assigned to the masterBirdSightingList property. The property has a copy attribute, though. it means the instance variable _masterBirdSightingList would be allocated for another space to preserve stuffs from sightingList. Why? Why not directly allocate space for the property like this : ``` self.masterBirdSightingList = [[NSMutableArray alloc] init]; ```