Question

if we use a property without the “retain”, what does it change? i have this example :

@property (nonatomic, readonly) CLLocationCoordinate2D coordinate;  
- (id)initWithCoordinate:(CLLocationCoordinate2D) coordinate;

in the .m :

-(id)initWithCoordinate:(CLLocationCoordinate2D)coord{  
    coordinate = coord;  
    return self;  
}

the “retain” is normally used for the setter, isn’t it? so here, we use the setter, in initWith…, but we don’t use “retain”… any idea?

Thanks

Answer 1

CLLocationCoordinate2D is not an Objective C object, so attempting to send retain and release to it doesn’t make sense.

 @property (nonatomic, readonly) CLLocationCoordinate2D coordinate; 

This declares an assign read only property, which is the only correct thing to do for a property with a plain C type. Additionally you have said it is nonatomic which means that there is no code to synchronize the property. Since the property is a struct consisting of two 64 bit values, that probably means that you can get an inconsistent result back if you read the property at the same time as some other thread is changing it.

the “retain” is normally used for the setter, isn’t it? so here, we use the setter, in initWith…

No, you don’t actually. The line

coordinate = coord;

actually assigns the instance variable directly. However, this is what you want in this case. If the property was not read/write and was an Objective-C object type, it would still be assigning the instance variable directly. In that case, you’d need one of the following.

[self setCoordinate: coord];

or

self.coordinate = coord;

or

coordinate = [coord retain]; // in init only

---

By the way, your init is wrong. It should follow the pattern:

-(id)initWithCoordinate:(CLLocationCoordinate2D)coord{ 
    self = [super init]; // assuming init is the designated initialiser of the super class
    if (self != nil)
    { 
        coordinate = coord;
    }
    return self;  
}