objective-c 引用计数

The rules are simple:

• Any object returned by alloc, copy, copyWithZone, or new has a retain count of 1.
• retain increases the receiving object's retain count.
• release decreases the receiving object's retain count.
• autorelease tells the current autorelease pool to send the receiving object the release message “later”.
• Any factory method that doesn't have “new” or “copy” in the name (e.g., stringWithString:) returns an object that it has autoreleased on your behalf.

Or, digested a bit:

• Any method whose name contains copy, alloc, retain, or new returns an object that you own.
• Any method that doesn't, returns an object that you don't own.
• To own an object, retain it.

The incorrect implementation of setName: that you show is incorrect because it stores an autoreleased object in an instance variable, when you mean to own the object. You should retain it or, in this case, copy it. One way is to simply use alloc and initWithString:, as in the correct example you show; the other way would be copy.