Question

Why does this work:

self.array = newArray;

But this doesn’t:

[[self mutableArray] addObject:object];

Meaning, why do I need to init the NSMutableArray for it to work when I don’t have to init the NSArray?

EDIT: Hops this is clearer guys.

Interface:

@interface Foo : UIViewController {

}

@property (nonatomic, retain) NSArray *array;
@property (nonatomic, retain) NSMutableArray *mutableArray;

@end

Implementation:

@implementation Foo

@synthesize array;
@synthesize mutableArray;

- (void)viewDidLoad {
    [super viewDidLoad];
    self.array = [Class returningAnArray];
    [[self mutableArray] addObject:objectIHaveOmittedTheCode];
}

@end

Answer 1

self.array = newArray;

In this line, you are assigning already created object to self.array. So, you’ve no need to create it.

[[self mutableArray] addObject:object];

But in this line you are trying to add an object to a array which is not created actually. If you don’t create the array, it will be nil, and sending message to nil won’t take any effect.