Question

Say I have the following function that returns a CLLocationCoordinate2D, which is just a struct that has two doubles (named longitude and latitude) in it:

- (CLLocationCoordinate2D)getCoordinateForHouse:(House *)house
{
    CLLocationCoordinate2D coordToReturn;
    coordToReturn.latitude = // get house's latitude somehow
    coordToReturn.longitude = // get house's longitude somehow

    return coordToReturn;
}

Can I basically treat this struct just like any other primitive type? For instance, if I call the function above in code somewhere else like this:

CLLocationCoordinate2D houseCoord = 
       [someClassThatTheAboveFunctionIsDefinedIn getCoordinatesForHouse:myHouse];

The value that was returned from the function is simply copied into houseCoord (just like any other primitive would act), right? I don’t have to worry about the CLLocationCoordinate2D ever being destroyed elsewhere?

Seems obvious to me now that this is probably the case, but I just need confirmation.

Answer 1

This is an area where Objective-C inherits its behaviour directly from C — assigning structs causes a shallow copy. So if you have any pointers inside the structs then you’ll copy the pointer, not the thing pointed to. In C code you need to factor that in to your adhoc rules about ownership. In Objective-C the automatic reference counting compiler isn’t capable of dealing with references to objects within structs (or, I think, unions) so it’s smart not to become too attached to the idea in any event.