关于self.和不是用self.的区别

// assign 
-(void)setMyObject:(id)newValue{ 
    _myObject = newValue; 
} 
// retain 
-(void)setMyObject:(id)newValue{ 
    if (_myObject != newValue) { 
        [_myObject release]; 
        _myObject = [newValue retain]; 
    }  
} 
// copy 
-(void)setMyObject:(id)newValue{ 
    if (_myObject != newValue) { 
        [_myObject release]; 
        _myObject = [newValue copy]; 
    } 
}