simple question about passing around pointers to objects

FROM : Paul Archibald
DATE : Fri Jun 27 22:22:17 2008

Comrades:

I have experimented a bit with this, and I think I have something 
that works, but I would like to understand it better. I am reading 
the Hillegass book, but I don't really see an example of what I am 
tryng to do, although it seems like a very basic question.

The Question:
If I want to create an object and pass it to another method, where I 
plan to use it briefly (as a local variable), what is the proper way 
to allocate and deallocate the object in the various methods?


Here is a simple example:

-(NSArray*) makeObject {
   NSArray *a = [NSArray arrayFromObjects];someObject, anotherObject, 
nil];
   // should I [a retain];
   // or [a release];
   // or [a autorelease];
   // or do nothing
   // before I
   return a;
}

-(void) useObject {
   NSArray *local = [self makeObject];
   // should I [local retain];
   // or [local release];
   // or [local autorelease];
   // or do nothing
   // before I exit this method?
   // I need to pass local as an argument to the creation of another 
object before exiting
   MyObj *o = [[MyObj alloc] initWithArray:local];
}


There are a lot of possible combinations here, and I have tried a 
bunch of them. Some of them work, others crash the program with a 
EXC_BAD_ADDRESS. But, as I have been trying to make an exhaustive 
test of what "works" and what "crashes", I realize that just 
experimenting with this is not enough, and I need a better 
theoretical understanding of this stuff. If you recognize this 
pattern and can tell me where to read more on it, that would be 
great, too.