From: Jeff Garland (jeff_at_[hidden])
Date: 2002-04-17 09:45:27
> The library suffers from a fundamental design flaw: it doesn't separate
> the concepts of "time" and "calendar". Time intervals and points in time
> are natural physical quantities that should be manipulated independently
The civil calendar (in particular local time) is governed by the rules of legislators not physics.
> of the units we choose to measure them with. The approach taken by the
> "GDTL" (I don't think there's anything "generic" about it) would lead to
> an explosion of mutually incompatible sub-libraries for every calendar
> anybody wanted to use.
GDTL doesn't try and 'force' radically different date/time systems into the exact same mold. Rather
it is an attempt to build constructs that enable rapid construction of new and consistent date/time
systems. I believe sub-libraries is exactly the right way to handle this because the rules,
constraints, and usage of these libraries is sufficiently different that it demands independent
> A date/time library should have types representing "point in time" and
> "time interval"; these would be opaque, with operations for arithmetic
> on them but no intrinsic connection with any kind of human calendar.
> Then you can add "calendar" types that represent a broken down time
> represented in a specific calendar. The calendar types would have no
> arithmetic properties themselves; they exist only to handle the
> conversion between the opaque time types and calendar-specific
Well we think about it a bit differently. The calendar or time_system provides the arithmetic
rules, types, and broken_down types for each system.
> Building Eurocentric assumptions into the language is exactly what the
> likes of Unicode and C++'s locale system have been developed to get rid
> of. I strongly believe that any proposal that doesn't separate the real
> physical concepts and their culture-specific representations into
> orthogonal components should be automatically rejected.
Physical concepts are one domain and civil time concepts are another. Date-time systems must handle
> On a tangential note, I also suggest that the concept labelled "time
> period" in the GDTL doesn't belong in a time library. It's a generic
> concept that would be better modelled as a template that can be
> instantiated on arithmetic types.
True, the concept could apply beyond time periods and the template does work for things other than
times. I'd could happily go elsewhere if we have a place for it. There are some other things in
the library that might fit into that category as well such as wrapping_int.
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