If your mutable thing is mandatory, then I think it should go first. Otherwise, you will be in a strange position when there are default arguments. The mutable

If your mutable thing is mandatory, then I think it should go first. Otherwise, you will be in a strange position when there are default arguments. The mutable thing would then be sandwiched between immutables. Of course if your mutable parameter is optional, it must be after all the required parameters. The argument above applies neatly to assembly instructions, which generally change one thing.