alt Hacker NewsWho else uses the proleptic Gregorian calendar other than programmers of datetime libraries?
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Considering it only diverges from the standard Gregorian for dates more than 400 years ago, it's not super relevant. Most people don't think about it. But it made a lot of sense to do the shift at the time. All recorded dates up to that point had been physically written down, so it would have been infeasible to migrate those all to the proleptic. If computers had been around, maybe things would have been different.
Fun fact: Greece was still using the old Julian calendar as of 1928, so it's entirely possible that you'll see dates on relatively recent Greek documents that are up to 14 days off from the calendar the rest of the world was using. Civil timekeeping is just a mess.
Who writes computer programs that deal with pre-1582 _dates_ at all?
In science-related code, I can image a case for calculating things like seconds elapsed across a very long time period. But in that case you're not really dealing with dates. Instead, you want something like the Unix epoch, but probably with an earlier epoch start.
There may be some very niche cases for pre-1582 dates in code that I'm not thinking of. But I'd expect that in this case you're going to put a lot of effort into finding the right libraries, or you might just write your own code.
Regardless, the linked blog post says of DateTime: "Unfortunately, like Python, a proper error message for impossible Gregorian dates is notably absent."
But this is just wrong. There's no "proper error message" to emit. The code works as documented.
It's typically not used in modern historical writing when referring to events located in areas that used the Julian calendar at that time.
But it is typically used when referring to events located in areas with no calendar system familiar to modern readers, most notably the Maya calendar. Maya Long Count dates are typically converted to the proleptic Gregorian calendar.
Also, many modern historical writings will display both Julian and Gregorian dates, particularly for dates around when the calendars were changing or when context is unclear (e.g. a historical figure who was born in an area with one calendar and died in an area with another calendar).