I think that "Instant" and "Duration" should simply be declarational roles that
don't have any implementation code to compose.
Composing "Instant" or "Duration" into a type simply says that the objects of
that type represent a point on a timeline or an amount of time.
Specific units, even "seconds" should not be mentioned at all in the definition
of "Instant" or "Duration"; instead, any particular units or calendars or
whatever would just be a property of the composing class.
Said 2 roles would *not* specify that values would numify or strify or boolify
in any particular way, such as seconds or otherwise; this is strictly a property
of the composing class.
Said 2 roles could define particular methods such as, assuming we're just
talking one-dimensional:
Instant - Instant --> Duration
Instant + Duration --> Instant
Instant - Duration --> Instant
Duration + Duration --> Duration
Duration - Duration --> Duration
Duration * Numeric --> Duration
Duration / Numeric --> Duration
Duration / Duration --> Numeric (rational in general)
Duration div Duration --> Numeric (integral)
Duration mod Duration --> Duration (rational in general)
I don't see that multiplying a Duration, or having arbitrary exponentiation,
makes any sense when talking one-dimensional, especially when we're being
completely units-agnostic. A specific implementing type may have a concept of
dimensionality, but I would think that these 2 roles don't.
Perhaps a suitable analogy is to look at the level of abstraction that "Numeric"
has relative to composing classes.
Do we want Instant and Duration to include concepts like dimensionality, such as
like Numeric may include Complex, or do we want it to explicitly be
one-dimensional (though units agnostic), like Real?
And whatever choice we pick, maybe there should be suitable generic names given
to the complementary concept of what I mentioned.
-- Darren Duncan
