I would definitely avoid this kind of shortcut, since they add basically no gain due to the copy ctr called immediately inside the method. I'd therefor suggest to drop the unnecessary copy (if it is necessary, then it's the ```const``` that has to be dropped) and fix the code inside the method accordingly. I suppose most of the problems could raise from the operator[] to access elements, since this will naturally break the const attribute. I'd use the at(key) one, which has a const flavour available. After a quick look at the code, I think this is the best solution.