Re: [boost] [date_time] boost time lacking tic-tac

From: James Porter (porterj_at_[hidden])
Date: 2008-05-22 17:16:39

On Thu, May 22, 2008 at 3:56 PM, Joachim Faulhaber
<afojgo_at_[hidden]> wrote:
> Incrementability seems also more fundamental to me than Addability.
> Which is to say that a concept or algebra that offers Addability
> almost certainly also has a Incrementability, but not the other way
> round. Take for instance the Peano Axioms of natural numbers, where
> Incrementability is given in the form of the fundamental successor
> function.

Not necessarily true. Strings under concatenation (a monoid) are
Addable, but incrementing makes little sense. Further, incrementing on
even the real numbers doesn't necessarily make sense, at least not
when defined in terms of the successor function (which maps integers
to integers). Complications also arise in, well, complex numbers. ;)

Dates/times are a more unusual case because their underlying
representation is integral, but as a physical concept they are
continuous (as far as we know). Questions arise especially when
considering the granularity of the date/time you are dealing with. Is
foo_date+1 24 hours from now, or one second from now? Or perhaps one
millisecond...

I don't think incrementability is as simple as incrementing the
private member of the date_time object.

- Jim