Question

I have read many posts about this now but I do not still understand it. I would appriciate an answer rather than a link because I probably already have read it.

if (self = [super init]) {

}

return self;

When I am calling the [super init] I know I am calling the method on “self”(the objects address) but I am starting the “method-search” in the superclass. When this returns I assign the object type id to self…This is where I am getting lost.

Am I assigning “self” as an initialized object up to the point of the superclass to self..?

I understand that I am doing this check to stop the initializing if the superclass implementation of the initializer returns nil however I dont understand what I am assinging to self….I thought self was an address to the current object in memory.

Thanks in advance

Answer 1

The assignment has always seemed a bit hacky to me. Its main point is that the superclass might want to return some other instance than the one that was initially allocated:

id foo = [[Foo alloc] init];

@interface Foo : SuperFoo {…}
@implementation Foo

- (id) init
{
    self = [super init];
    if (!self)
        …;
    return self;
}

@interface SuperFoo : NSObject {…}
@implementation SuperFoo

- (id) init
{
    [self release];
    return [OtherClass alloc];
}

This is crazy indeed, but the fact is that [super init] might return an object different from the previous self. See Mike Ash’s blog post, that should make things super clear.