You are thinking about both dates and appointments the wrong way. Dates never change, they are fixed points in time. A date is not an appointment; an appointm

You are thinking about both dates and appointments the wrong way. Dates never change, they are fixed points in time. A date is not an appointment; an appointment has a date associated with it, and many other things. Appointments do not change either: they are canceled and rescheduled (which means making a new appointment). The problem with C and C++ having the const keyword is that it is overly restrictive and is not flexible enough. What you are trying to express with const is that the value of an object before a computation is equivalent to its value after the computation, under some definition of equivalence. What const actually says is that the object will not change at all. C++ tries to mitigate this with mutable, but this is too rigid: the same things are mutable or immutable regardless of the context. What we really need is what you see in specification languages: the ability to declare precisely how a value is modified by an operation. Maybe I have an object with a stream member, and I want to say that nothing will be written to the stream without saying that the stream will not flush its buffer for one operation, whereas in another operation I want to ensure that the buffer will not be flushed.