Does lastObject in NSMutableArray return a copy of the object?

问题

I have a question related to this piece of code

NSNumber *lastObject = [self.myStack lastObject];

if(lastObject){
    [self.myStack removeLastObject];
}

return [lastObject doubleValue];

I am surprised that the lastObject is still in memory despite getting removed. How is this happening? Is it that lastObject returns a copy of the object?

回答1:

No, it's not a copy, it's just autoreleased. It will be released in the near future.

EDIT: to clarify - on [self.myStack removeLastObject], the object is sent release immediately, but you got an autoreleased pointer from [self.myStack lastObject] so the array is not the last owner of the object.

来源：https://stackoverflow.com/questions/9354215/does-lastobject-in-nsmutablearray-return-a-copy-of-the-object