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Methods:

  alloc               - allocs memory for the object, returns pointer to it, sets refcount to 1

  release            - decrease refcount, sends dealloc if refcount is 0

  retain              - inc refcount

  copy               - returns a copy of the object with refcount 1

  autorelease      - add object to current autorelease pool. Later pool will send release method to the object

  retainCount     - returns refcount

Allocation and free:

NSString *s = [[NSString alloc] initWithString: @"hello"];

[s release];

Function that returns allocated object must use autorelease pool because the method doesn't own the memory but can't 

-(NSString *) returnAllocatedString {

  NSString * str = [[NSString alloc] initWithString: @"test"];

  return [str autorelease];

}

Autorelease pool schedules release messages for later:

* only one at a time (current autorelease pool)

* created automatically by NSApplication object (create manually if not using NSApplication)

* when receives release message, calls release on its objects

* NSApplication sends release at the end of event loop iteration

* can create autorelease pools with smaller scope (per method, in a scope) for performance and memory size (so that global pool doesn't grow too big)