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Comment by gberger | Hacker News Reader

'Falsehoods programmers believe about time: - Every day has a sunrise and a sunset'

Falsehoods programmers believe about time:

The fundamental one is: "I'm so very clever, and I've dealt with dates my whole conscious life, I can probably think of all of the edge cases off the top of my head!"

I think you're right, but that the tone I read in your words would prevent people from improving.

Rather than "I'm so clever" it is more "this isn't complicated". One can argue they mean the same thing, but I'd say they mean different things if comparing to an outside scale. The solution to thinking you're so clever is to reduce your arrogance, but the solution to thinking problems are simple is to stop assuming any problem is simple.

My favorite incorrect fact is that there are 24 timezones. In fact, the number of offsets from UTC fluctuates throughout the year (at least last I worked on scheduling in 2012. Back then it was either 39 or 40 depending on DST)

That becomes fairly obvious when you consider Arizona doesn't observe DST, but Utah is the same longitude (lies directly north) and does observe DST.

Yep. And there also small regions that observe daylights savings WITHIN regions that don’t observe daylight savings WITHIn regions that do observe it. For example, in Indiana it is on a per county basis[1].

1. https://www.timeanddate.com/time/us/indiana-time.html

Speaking of within, I fibbed slightly about Arizona.

https://en.wikipedia.org/wiki/Time_in_Arizona

The Navajo Nation is within Arizona's boundaries, and it does observe DST. And the Hopi Reservation is within the Navajo Nation, and it does not observe DST.

And since Arizona is surrounded by California, Nevada, Utah, New Mexico, and Mexico, all of which do observe DST, that means you have an island of no-DST (Hopi) inside an island of DST (Navajo) inside an island of no-DST (Arizona) inside an area of DST (adjoining US states plus Mexico).

Well that's almost enough to make one think daylight saving time is a bunch of cracked-up nonsense!

How did we screw up time zones so much?

We invented and then implemented time zones and then invented and then implemented daylight savings time; arbitrarily and with arbitrary laws and treaties.

There are days where I think I should go back to a mechanical watch and adjust the time each day at high noon. It won’t agree with anyone else’s time most of the time, but at least it will be correct.

But won't it be wrong as soon as you start travelling east or west, though?

Somewhere I have an old book which includes time zone maps for Indiana in the 50s and 60s. Every single year there were changes.

Yeah I always feel like a jerk when people open tickets in the summer saying “Please do this at #:## EST” and I have to reply “thanks for providing a time but it’s currently EDT in NYC. Is that what you meant?”

I hear you. It almost always is what people meant but most of us (myself included) rarely think about the distinction.

I've just gotten to saying ET (or equivalent) all year-round .

That’s the battle I fight: persuading people that saying “Eastern” is accurate and sufficiently precise. Precise and inaccurate is a bad combination.

No reason to be snarky with people. They mean whatever time it currently is or will be.

Are you sure though?

If they copied that date from some automated system it might as well be any of these.

Humans usually say “New York time”.

In my experience, humans never say "New York time", or "San Francisco time", or anything like that, they say "EST" and "PST" regardless of whether daylight saving's is on.

I'm guilty of this too, since I can never remember which part of the year constitutes "on" and which is "off", only where the boundaries are. If I stop and think I can usually remember "spring ahead is turning it on", but never off the top of my head.

That's only slightly worse than how I feel when people say that something's happening in the summer when it's actually winter where I live.

DST rules are just insane. I'm responsible for some code where I just drew the line and 40 some odd people in one of the Antarctic stations are just going to have to live with wrong time part of the year if they ever run my code. I'm not adding another code path and test case just because these people wanted their own special concept of time. I don't remember the pattern, but I think it was maybe a daylight savings time and then an extra one stacked in the middle.

We have endless problems with DST as well. I can't wait for the EU directive that abolishes it. Russia dropped it years ago. We'll still have to support past times and other timezones though.

I wonder how long time it will take to forget DST if it is abolished. Will that messy spaghetti code be ripped out and never seen again.

Most standard libraries still have support for the Julian calendar. That stuff is never going away.

I doubt it's "most". Python, Javascript, and C++ don't seem to. The only ones I found that do seem to are C# and Java.

I just got a ruby gem from someone who actually made tables on the stuff. I made a script that cut out far past and future times to lower loading time from 10m to 30s and figured I could upgrade the gem to leverage an expert’s research as timezones changed (e.g. India changing zones)

Julian calendar is still used by the US Navy. Every supply department office you go into has a conversion table up on the wall.

And that it's possible for two places to be more than 24 hours apart.

There's also half hour timezones, found at least in India, and I think a couple quarter hour zones.

but that the tone I read in your words would prevent people from improving

Are people really that fragile? Yes and no.

The solution to thinking you're so clever is to reduce your arrogance, but the solution to thinking problems are simple is to stop assuming any problem is simple.

Isn't humility the answer to both? Someone should develop a humility course for programmers involving an "ultra drone," writing the date/time library for it, and some simulated world test cases. Such "humility exercises" are found in various disciplines. There's one for CIA analysts, involving analyzing US Civil War sites via sat photos, then having them visit in person.

> Are people really that fragile?

It's not fragility, so much as perspective.

When you are thinking something is simple, and you say "Am I'm thinking I'm impressed with my own cleverness?" it's easy to say "no". Because it's not arrogant to think you can accomplish something simple.

When you are thinking something is simple, and you say "Am I assuming simplicity?" it's easy to say "yes".

Realizing you're committing the fallacy is the first step to avoiding it.

Right? I am reliably put into this weird emotional state of being simultaneously entertained and chagrined at the propensity for technologists (and I very much include myself in this criticism) to make these kinds of assumptions, and the edge-case bugs that fall out of them.

And it's a reminder that "edge case" is relative. It's not an edge case for people who live there!

If we tried to get these thing 100% right we'd not have time for anything else. Punting is pragmatic.

You're absolutely right that "100% right" is an unreasonable standard. I submit that knowing that there are places on the planet where, at times, the sun doesn't set, however, is a reasonable thing to expect of someone who's made it far enough in life to be writing code (or testing it! How did this pass QA?) for Apple.

f.lux gets it right if I set my zip to Barrow, AK. Why can't Apple, with how many orders of magnitude more resources at their disposal — including knowledge?

Agreed

It exists, it's just complex-valued.

True that

(Posted at (5+4i):(37+5.23812i) AM)

Where does j & k fit into your quaternion representation?

There are both coordinates and rotations, it would probably be better modeled as a quarternion or something of an even higher order.

I believe you can actually compute the sunrise time of a location/day that doesn't have a sunrise, and it would be just a complex number (root of some analytic function).

Aside from having a falsehoods checklist that includes this, how would this be caught by a programmer who isn’t mindful of the fact that you don’t always have a sunset?

Consider the loop conditions (which are clearly non-trivial) and ask "is it certain that this loop will always terminate"?

Presumably in this case you would have arrived at an answer along the lines of "yes, so long as there's always a sunset". Which should then prompt the question: hang on, is there always a sunset? A quick scan over whatever datafile it's using for input should answer that.

Falsehood #2: Every day starts at 12:00 am midnight.

Wot, what's the false case?

DST. Some countries (Brazil) switch over at midnight instead of 2:00 am. One day of the year has no midnight.

I never considered how many logical problems arise from the use of AM/PM. I knew time handling is tricky but it seems like every time I see this topic discussed, I learn about a new corner case.

Some cultures end the day at (wait for it...) sunset.

And now we're back to the original problem.

Apparently Muslims and Jews here have agreed that the day ends at sunset or at 21:00, whichever comes first (or at all). It would be difficult if you couldn't eat for the better part of a month.

Because there is neither a 12:00 am, nor a 12:00 pm. One is 12 noon, the other is 12 midnight.

AM and PM are "ante meridian" and "post meridian": before" and after. But 12 is on* the meridian; neither one. You can meaningfully say 12:00:01 am, or 11:59:59 pm, but for 12 sharp nobody can say whether am or pm is dark or day.

Airlines schedule flights at 12:01 for this reason.

Meridian in this context is noon. 12 “anti meridian” is 12 hours before noon. 12am. Which is exactly correct.

I’m no domain expert but I’m guessing flights are scheduled at 12:01am because people are bad at time. For instance some people would think 12am is the last minute of the previous day instead of the first minute of the next day. 12:01 removes the potential ambiguity.

12 "post meridian" is 12 hours after noon. 12pm. Which is midnight. But you don't use 12pm to mean midnight. Why not? Midnight doesn't actually belong to a day at all. Our current conventions of 12am and 12pm seem to be mostly products of digital time keeping.

Nitpick but since we’re talking about time: AM means “ante meridiem”, as in “before”. Not anti as in “against” :)

You've just completed GP's point perfectly though - 12 hours after noon (post meridian) is midnight too.

OU4483 leaves CPH at 1200, as does another flight.

There isn't a flight at midnight, but there are fewer flights then anyway, and it may be confusing to some which day the flight is on. Of course, the flights around midnight have departure times of 2350 and 0015.

This is the reason 24hour clock is the way to go. 23:59, 00:00, 00:01, ...

0 was invented for a reason. This am/pm stuff is so confusing.

credit to /u/gwern

Time is hard: https://zachholman.com/talk/utc-is-enough-for-everyone-right

This is all because of the fact that we're trying to represent the time taken by the earth (an arbitrary planet that has no impact on the universe whatsoever) to revolve around the sun (an arbitrary star) in terms of the amount of time the earth takes to rotate around itself. These two obviously unrelated things are somehow merged into to create an unsolvable clusterfuck. To make matters worse, let's sprinkle some politics...

> (an arbitrary planet that has no impact on the universe whatsoever)

What do you call this type of worldview where you just view everything as completely meaningless or devoid of any value? Is it really straight up Narcism? I mean my god no wonder this is one of the most depressed generations on record.

Apologies for the off-topic comment, I just felt compelled to post this. We are the most meaningful, most important things in the universe until we know or learn otherwise. We are the most intelligent, most accomplished life forms in our known existence. Viewing it as arbitrary might be "technically true" but then again what do we know? What if we are it? It is just as plausible as the other view: that we are just on a billion year course for the eventual heat death of the universe and the end of existence all together.

Treat yourselves as special, you are. Treat others that way too. You'll also be a lot happier. Sorry for the platitudes.

If I remember correctly the word you're looking for is nihilism.

Ironically, viewing yourself as the most meaningful, important, intelligent, accomplished thing in the universe sounds a lot like narcissism.

When your "universe" is the size of a solar system with a single life-supporting planet, what other conclusion could possibly be met?

If you're the only one in a talent contest, you're the best ... and the worst.

I like life, but we are meaningless motes in the universe. We'll all be dead one day and no one will remember us.

It's ok though, it doesn't matter.

If human matters do not matter, why assume that language carries meaning?

Do you believe that animals have meaningful conversation? Or that humans do?

Does the universe speak? If it did, would you know?

Do you understand its language? Can you hear it?

There's also something else: nothing.

I've learned to enjoy the struggle and this has helped me immensely.

It’s not an arbitrary planet from our perspective, which is the only one we even know to exist.

We’ve needed to coordinate actions forever and the sun was the only reliable way to do that for a long time. Nothing arbitrary about where our time came from.

Sure, for now; but I feel like it'd be aesthetically pleasing in some sense to try for something more objective—i.e. to predetermine the sort of timekeeping methods we would need upon establishing trade relations with a universe full of aliens, and then to use those methods in advance. Like a Society for Creative Anachronism meeting where the target period is forward in time rather than backward.

Given that we have no idea whether aliens even exist — and that life on Earth both literally and figuratively revolves around the Sun — that strikes me as the ultimate premature optimization.

If we ever meet aliens that also happen to be advanced enough to trade with, we will have already solved this issue ourselves because we’re cruising around in the Enterprise and needed a new timekeeping system by that point, or the Enterprise came to us and they will have their own timekeeping system that we can adopt.

Before then? Eh. Objectivity is overrated and an imperfect time system is a nice reminder that life doesn’t revolve around us and what we want.

I was hoping that he'd cover the different kinds of time, and where each kind is used in a program, but nobody seems to think about it:

* Absolute Time: A time value fixed to UTC.

* Fixed Time: A time value fixed to a specific time zone.

* Floating Time: A time value that is interpreted according to the time zone of the observer.

https://technicalsourcery.net/posts/time/

This is true, depending on how far away you look from where you are.

Or, this is true, if you allow that "day" is defined by sunrise to sunrise (or sunset to sunset, depending on your religion), which in the region discussed would give you one sunrise per revolution around the sun.

Either one of those truths could be the basis for fixing this bug.

EDIT: Rather than a bug (in the implementation), this may be better classified as an under-specification.

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