What's the point of this in objective-c

Question

SomeObject *temp = [[SomeObject alloc] init]
self.theObject = temp;
[temp release];

Why is it always done that way? Why not

self.theObject = [[SomeObject alloc] init];

Answer 1

The second version leaks the SomeObject instance, since self.theObject will call a setter that, if properly written, retains the object.

You could just do

theObject = [[SomeObject alloc] init];

and some people certainly do. Others prefer to always use accessors though, either for consistence or to avoid bugs if the accessors have side effects (for exmaple, you would be bypassing KVO notification, which could be a problem if it's not part of an init method).

Answer 2

If the theObject property is a retaining property, the first way is correct, because it doesn't leak memory. It's also more efficient than the correct way to write the second version, which is this:

self.theObject = [[[SomeObject alloc] init] autorelease];

Whenever you create an object with alloc you're in charge of releasing it somehow, whether by release or autorelease.