To answer my own question a couple of days later, I suppose that if they secretly shadow the mutated var name with a new longer value (in this case) on the stac

To answer my own question a couple of days later, I suppose that if they secretly shadow the mutated var name with a new longer value (in this case) on the stack -- perhaps that is what is meant by "a projection". In that case, no new allocation would occur, since the stack is already allocated. I'm not a language or compiler expert, so maybe this terminology is well know in those circles.