When ever i see "never implement your own...", i know i want to implement it myself. People say that about hard things, and I only want to do hard things. Nobody wants people who can do easy things, people want people who can do hard things. The only way to learn how to do hard things, is to do hard things, so do the hardest things.
So go ahead, write your own date library, your own Unicode font rendering, compiler, OS, game engine or what ever else people tell you to never do because its hard.
glibby · 1h ago
By all means, write it. Just don't use it. These warnings are almost always in the context of code you're going to release, not exercises in learning on your own.
flir · 22m ago
In the case of date libraries, I think if I ported the tests from a few well-known libraries to my own, I'd have reasonable confidence in my own.
Having said that, I don't think date libraries are hard, I think they're messy. Mostly because humans keep introducing convenience fudges - adding a second here, taking eleven days off there, that kind of thing.
ramijames · 1h ago
This is such nonsense. All the stuff that we use, someone wrote. If nobody makes them, then how is that going to work?
The messaging here is that you should be careful about using what you build on your own because it:
- hasn't been battle tested
- likely has bugs
- isn't mature
The only way that it will be all of those things is if someone invests time and energy in them.
From an ecosystem perspective this is absolutely the right thing. You want duplicate projects. You want choice. You want critical knowledge to be spread around.
Swizec · 1h ago
> If nobody makes them, then how is that going to work?
I see it as “Dont write your own X, unless you want to maintain X. Here be dragons, this problem is deeper than it appears, the first 80% will be easy, the next 15% will annoy you, and the last 5% will consume your life for weeks, months, or even years. Or you could use a library”
mattmanser · 54m ago
It's about exposure.
The things that people write that everyone uses have had HUGE exposure.
They've been exposed to all the edge cases, they've been tested millions, if not billions of times. All the bugs ironed out.
The people who've worked on them are now the greatest domain experts on that little corner of comp-sci.
Yours won't unless it hits prime time.
So yours will be weak, brittle and dangerous.
gmueckl · 28m ago
In order to have these mature libraries, someone hat to start building them. They all had to to be incomplete, immature and horribly buggy early in their lifetime, too.
DANmode · 55m ago
Holy shit.
The point is, before you release your new thing, make sure it addresses all of the pain points the previous solutions have already slogged through,
or that if it doesn't, people are still aware of when they can arise, and why your thing has chosen not to mitigate them yet,
or ever, if it's an opinionated piece of tech.
commandlinefan · 31m ago
Nah, finding that stuff is what users are for.
leakycap · 1h ago
I get wanting to do hard things, but do you write in binary? Do you crank your own electricity?
My most valuable resource is time. Sure, I could learn more low-level aspects of my craft ... and sometimes I find it useful to do so.
When I focus on doing the hardest, already solved things by re-implementing them my own way, what value am I adding?
I've never met a client who cared about a library or how I did something in code - until it broke. Then, they didn't care who wrote it, they just cared it started working again.
ok_dad · 18m ago
People have built tables but I still build tables myself. Not as many people will use them as people who use IKEA tables, but that’s okay, I’m still going to build them.
VohuMana · 50m ago
I think in the case of the article the date library isn't necessarily hard but tedious. They mention most date libraries suffer from supporting too many standards or allow ambiguity.
I agree with you though, do the hard things even if it doesn't work 100% right you will have learned a lot. In university I had to implement all of the standard template library data structures and their features, it wasn't as robust as the actual STL but the knowledge of how those work under the covers still comes up in my day to day job.
qwertox · 1h ago
This past 22nd of July was the shortest recorded day [0]. How would your library handle this?
Answer: not at all, unless I had to deal with astronomical time to compute locations of celestial bodies with high precision.
david-gpu · 42m ago
Software companies make money by providing value to their customers via the software they provide. How does reimplementing a hard but already well-solved problem align with their goals? How does that compare with solving a hard problem for which there are no good solutions yet?
bobsmooth · 1h ago
Solve new hard things instead of solved hard things.
fsckboy · 1h ago
you want to do something people really think is hard? use C. it's not safe.
quelsolaar · 1h ago
I exclusively write in C89. I'm a member of the ISO C standard board.
davidw · 3h ago
It's like that joke someone posted on Twitter: "I was in favor of space exploration until I realized what it would mean for date/time libraries"
3cats-in-a-coat · 3h ago
Every time someone mentioned "days" or "months" or "years" in Andor I had to mentally zap my brain not to think about how it doesn't make a sense across a galaxy.
jerf · 2h ago
Consider it a translation convention. There's a time and a place for "cycles" or "rels" or whatever, but it gets into "Calling a Rabbit a 'Smeerp'" [1] territory pretty quickly. The payoff isn't really all that great.
Stargate SG-1 is one of my favorite instances of this. The first couple of episodes address the fact that the Earth characters do not speak the same languages as everyone else in the galaxy. Then, having established the point that A: the show runners understand this is an issue and B: it makes for a rather tedious watch, they moved on to "everyone speaks English" and we all breathed a sigh of relief. I just think of it as part of the "camera" now. It turns out that we don't necessarily want a truly literal recording of what such things would look like.
"The Hunt for Red October" had an interesting way of handling this with the Russian speakers. The movie starts with them speaking Russian with English subtitles, does a slow zoom into the Russian-speaker's lips, and switches to English mid-sentence.
commandlinefan · 26m ago
Like in Game of Thrones when Davos was trying to learn to read and incorrectly pronounced the word "knight" the way it was spelled - somehow I could accept that everybody in a fictional universe spoke English except for all the ones who spoke other fictional languages, but I drew the line at words being spelled the same as well.
tetha · 2h ago
I think that these fundamental things can be turned into an interesting topic, but you have to try for it.
Like, in a story background I'm pushing around, there's a coalition of a large amount of species developed on different planets. And you're a military officer, and you need to coordinate shifts, but - assuming some collectively normalized number of hours - some of your tiny dudes are tuned to 3 hours of sleep, 3 hours of leisure and 3 hours of work, others weird dudes with 2 arms and 2 legs are tuned to 38 hour cycles, and some huge dudes with a trunk in their face are tuned to 356 hour cycles.
Even if you could train and adjust this by an hour or two (which, for the 3 hour dudes would compare to an 8 earth-hour extension of duty for us), how the heck would you coordinate any kind of shifts across this? Or does every species have their own schedule? Good look finding crossover meetings then. Some of the small guys would have to do overtime for longer meetings even.
But you have to make it a point of the story and the challenges if you want to include it. If it is just a weird side note, just say that they figured out a conversion and that's it.
ceejayoz · 2h ago
> The payoff isn't really all that great.
If you’ve read David Weber’s Safehold series, this point gets super clear. It's written with names like "Zherald Ahdymsyn" (Gerald Adamson), but that makes it quite the slog for many.
clem · 2h ago
Vernor Vinge had it figured out in A Deepness in the Sky with the use of kiloseconds, megaseconds, and gigaseconds.
BurningFrog · 2h ago
A second is still originally defined as 1/86400 of an Earth day.
That doesn't make it unusable as a cross galactic time unit, and I think the same goes for years and hours.
gleenn · 2h ago
Case-in-point, you are mistaken. The duration of a day changes due to many things, both logically and also physically due to the nature of Earth. Also just because you can call a second a second doesn't mean that is helpful making datetime software usable or easy on a different planet.
mikepurvis · 2h ago
I think he's speaking historically. Obviously now a second is a fundamental SI unit defined in terms of physics experiments, but the origin of it was as the amount of time that was 1/3600th of an hour of which there are 24 in the day.
shadowgovt · 1h ago
Similar to how almost-pi-squared meters-per-second shows up in the constant for gravitational acceleration near Earth's surface because the meter was originally "the length of pendulum that ticks once a second" and there's a pi in the pendulum motion equation.
(... it's not exactly pi-squared because the French yanked it around a bit before settling into the modern number based on light in a vacuum and cesium atoms).
ceejayoz · 2h ago
Seconds are now (in SI) defined as calculated from behavior of cesium-133 atoms.
You can also define "days" and "years" in terms of that SI definition.
I don't think that helps with the original concern.
ceejayoz · 1h ago
You can, yes. But having it all stem from some fundamental constant value any civilization can handle permits translation between civilizations.
"Our dates start x trillion rotations of pulsar y ago and our unit is defined as z wiggles of cesium" is a starting point.
bunderbunder · 1h ago
9,192,631,770 is clearly a sensible number and not something that's blatantly chosen to match some arbitrary pre-existing geocentric standard like 10,000,000,000 would have been.
ceejayoz · 1h ago
It's retrofitted to what we already defined as a second, sure.
But you can tell an alien species our units are expressed in multiples of that, and they can translate it into how theirs works. (Vinge, for example, has space-faring humans talk about "megaseconds" and "gigaseconds" rather than days/years.)
layer8 · 2h ago
The issue is that planetary locales will each have their own days and years (and possibly hours), so it would be confusing to adopt that same nomenclature for an interplanetary/interstellar time unit. And since the latter will be inconsistent with local time systems anyway, it’s easier to just have it use powers of ten. At least until we meet aliens that may prefer a different base.
Well, that problem exists now too, but everybody sticks their head in the sand.
TheJoeMan · 3h ago
It's funny to reason why we must go to bed when the clock has a certain number, since modern technology could easily be programmed to adjust as needed. No technical reasons the Martians can't go to bed at 9:00am today and 9:40am tomorrow. This mirrors my thoughts on why farmers caring about daylight savings time is farcical, farmers I know use the timekeeping of "crack of dawn" and "sunset".
dmoy · 3h ago
iirc DST was never about farmers, and always about energy usage (lighting, etc) in the evening
Agree I've never met a farmer who cares about DST. Though also, for non-ag farmers, sometimes "crack of dawn" isn't early enough lol. Cow: "Dairy barn has electric lights, why aren't you awake at 4am tending to my needs, Human? Vacation? Lol no, stay here. Every morning. 4am."
Arainach · 3h ago
People want to understand when things are open/reasonable without having to do a lookup every time. A conversion has to happen somewhere - either I can say "X is in timezone foo. It's 1300 there so they're awake and I can call them" or "It's 1900 UTC, X is awake from....err....2200 to 1400, so I can call now".
The first is significantly easier as it requires remembering only a single offset and then going with societal conventions.
devilbunny · 2h ago
Farmers who have to buy things (and that's almost all of them) care about the hours the shops are open, which is affected by DST.
bluGill · 2h ago
And farmers are annoyed that one day the shop is open just after dawn, and the next not for another hour. Farmers are building their life around sunrise/sunset (or sometimes the dew cycles which is tied to the sun), and then fit the rest of the world in between.
johnnyanmac · 1h ago
We're mostly still a diurnal species. We go to bed at 9PM instead of 9Am for evolutionary reasons. We can fight against it, but the reasons are as arbitrary as biology is.
Likewise Daylight savings is a concept that had its uses, but makes less sense as technology progresses. I don't think even farmers care much about 7AM approximating to sunrise and 6PM as sunset.
jameshart · 1h ago
Time zones are less about having uniform names for the times for waking up or going to work or mealtimes, and more about when your calendar changes from one date to the next.
neilv · 47m ago
This article doesn't get into some of the special fun of ISO 8601, including relative values, non-Gregorian values, durations...
Some of the things in the standard are surprising, like maybe were a special request. At the time, I commented, something like, Somewhere, in the French countryside, there is a person who runs an old family vineyard, that is still stamping their barrels with the timepoint information [...]. And that person's lover was on the ISO 8601 committee.
(I once wrote an time library in Scheme that supported everything in ISO 8601. It did parsing, representation, printing, calendar conversion, and arithmetic. Including arithmetic for mixed precision and for relative values. It was an exercise in really solving the problem the first time, for a core library, rather than cascading kludges and API breakage later. I don't recall offhand whether I tried to implement arithmetic between different calendar systems, without converting them to the same system.)
QuadmasterXLII · 3h ago
I ran into date heck recently in a medical setting for storing birthdates. Eventually I settled on the idea that a birthdate isn’t a physical time, it’s just a string. We can force the user to enter it in the format 02/18/1993 leading zeroes and all, and operations on it other than string equality are invalid. We’ll see if this survives contact with the enemy but it’s already going better than storing and reasoning about it as a point or interval in time and people’s birthdays changing when they move timezones.
kaoD · 3h ago
I like how Temporal[0] does this. What you were dealing with is Temporal.PlainDate[1], i.e. a date with a calendar associated but no time or timezone (might be due to being implied but also might be irrelevant, like in birthdates).
Temporal has other cool types, each with distinct semantics:
- Instant: a fixed point in time with no calendar or location. Think e.g. "the user logged in at X date and time" but valid across the world for any timezone or calendar system. This is what we usually use "Unix UTC timestamps" for.
- ZonedDateTime: like an Instant but associated with a particular calendar and location. Think an Instant but rendered "real" into a calendar system and timezone so the user can see a meaningful time for them.
- PlainDate: already discussed. Think e.g. birthdates.
- PlainTime: think "run task every day at 6:30pm".
- PlainDateTime: like an Instant but associated with a calendar system, but no timezone. Think e.g. what a user would insert in a datetime picker, where the timezone is implied instead of explicitly selected.
- PlainYearMonth: think e.g. "we'll run our reports during October 2025".
- PlainMonthDay: think e.g. "my birthday is June 13".
- Duration: think e.g. "the task ran for 3hrs 30min".
yeah, it was a long (and painful) time coming, but i think the temporal api finally basically nailed it. you know a library is good when you learn something about how to think about the problem just from how the code/api is structured.
benreesman · 1h ago
Relatedly, std::chrono isnt exactly a beauty, but it did get people thinking about time points and durations and clocks and which operations are valid ways to move among them. Stuff like this is good.
legulere · 54m ago
If you store it just as a string it means that you cannot do anything useful with it like age-dependent logic or you just pass on parsing logic to users of the field.
FHIR in my opinion has a pretty good system for dates (including birthdates):
YYYY, YYYY-MM, or YYYY-MM-DD. (Not knowing your exact birthday is common for some countries).
I guess in your case you're never doing date arithmetic or greater than or less than, but only doing equality testing, right? That is, it's part of a composite key.
I faced a similar problem with a form where people were supposed to submit a date and probably not aware of what timezone was involved. I figured that so long as they selected "02/28/1993" and people always saw "02/28/1993" that was correct and if they ever saw it differently it was wrong. So I used non-TZ aware dates throughout the whole system.
8organicbits · 3h ago
> in the format 02/18/1993
Is this DD/MM/YYYY or MM/DD/YYYY? I can tell from the 18 that it's the latter, but that convention isn't universal. I'd recommend YYYY/MM/DD as a less ambiguous format, but I don't have a perfect answer.
kriops · 3h ago
Furthermore, require dashes over slashes to signal that you are expecting ISO-8601 compatible dates, i.e., YYYY-MM-DD. Most users does not know the standard even exists, but it serves as an affordance that it is different from dd/mm/yyyy, etc.
PaulHoule · 3h ago
Those ISO-8601 dates are great for date processing with primitive tools such as GNU sort or awk since they sort lexically, at least if you're not comparing dates in different time zones.
Yes, except for all the completely unhinged stuff in ISO 8601. You probably do not want to deal with durations, or repeating intervals, or even week dates and ordinal dates.
or a text field with some code that converts vernacular dates to a structured format. I don't think users are going to be too weirded out at seeing "1997-04-15" and will probably learn to use that natively.
The hard part is that a lot of devs aren't aware that there's a standard and that standard is superior to the alternatives.
senfiaj · 3h ago
Every time I see an input date string in XX/XX/YYYY format I get a micro PTSD flashback. This cannot be parsed reliably and is locale dependent. The standard date format is YYYY-MM-DD (it's also the date part of the ISO time format). Raw text inputs should be avoided as much as possible, date/time pickers should be preferred.
dragonwriter · 2h ago
> The standard date format is YYYY-MM-DD (it's also the date part of the ISO time format)
Strictly, it is the extended form of the ISO 8601 calendar date format. (The basic format has no separators.)
ISO 8601 allows any of its date formats (calendar date, week date, or ordinal date) to be combined with a time representation for a combined date/time representation, it is inaccurate both to call any of the date formats part of the time format, and to call the calendar date format the format that is part of the combined date/time format.
(There's a reason why people who want to refer to a simple and consistent standard tend to choose RFC-3339 over ISO 8601.)
hanche · 3h ago
Even worse with just two digits for the year! 01/02/03 could be 1 Feb 2003, or 2 Jan 2003, or 3 Feb 2001. Let’s just be thankful no one ever uses any of remaining three permutations.
jack_pp · 3h ago
Pretty sure they force the user into that format so that shouldn't be an issue
happytoexplain · 3h ago
This isn't really relevant to the parent's topic though, aside from UX. The UI can tell the user which is the day and which is the month. The logic layer knows the format explicitly.
BurningFrog · 2h ago
Normal/"legal" dates are not timestamps or related to timezones, and this fact will eternally be rediscovered as long as humans write software.
dragonwriter · 2h ago
What environment are you in where you have to work with birthdates, you have timezone aware dates, times, and intervals, but you don't have a naive/plain/local date type that already exists forcing you to use strings in place of date-without-timezone?
You seem to have a reasonably expedient solution for that problem, but it is surprising to have the combination of things you have to have and things you have to be missing to have that problem in the first place.
kccqzy · 3h ago
> people’s birthdays changing when they move timezones
That's because the developers use datetimes (aka timestamps) to store a single date. Just pick an arbitrary epoch date (such as January 1, 1900 as used by Excel, or my favorite January 1, 1600 since 1600 is a multiple of 400 making leap year calculations even simpler) and store the number of days elapsed since then. The rules involving leap years are much much simpler than rules involving timezones and timezone databases. The translation from/to this representation to a broken-down y/m/d takes only ~50 lines of code anyways.
Of course if you don't need to do arithmetic on dates, just store three numbers, year, month, and day.
SoftTalker · 3h ago
No, don't do that. Use a date datatype (not date/time). You aren't the first person to ever need to handle dates without times/timezones in a computer program. Use what your database/language/libraries already have to support that.
PaulHoule · 3h ago
Well, for hardcore chronology Julian dates are what you do.
which are the moral equivalent of Unix timestamps with a different offset and multiplier. These work OK for human history but will break if you go far enough into the past or the future because uncertainty in the earth's rotation adds up over time.
If you don't care about timezones timezones may still care about you, if you want to minimize trouble it makes sense to properly use timezone-aware Zulu (GMT) dates for everything if you can.
In certain cases you might be doing data analysis or building an operational database for throttling access to an API or something and you know there are 16-bits worth of days, hours, 5-minute periods or something it can make sense to work relative to your own epoch.
No comments yet
tadfisher · 3h ago
Specifically, a "local date", codified as LocalDate in every date library worth a damn, except for Javascript which chose "PlainDate" just to be different.
happytoexplain · 3h ago
In my humble opinion, this is not good advice unless you demonstrably need it for query performance or something. It is very easy for the logic layer to accidentally mess that up, either in reading or, worse, in writing back.
In this case, I'd suggest storing what you mean (the user wasn't born 9,487 days after Jan 1 1970. They were born Dec 23, 1995.)
Storing the literal units (and ONLY the relevant units), as the parent has, is robust and logically+semantically correct (they could add a translation layer for UX so the user doesn't have to be particular, but that's beside the point). Whether you use a string or a struct or some date-only type is moot, as long as you're literally storing the year, month, and day, and only those three things. You can ephemerally convert it to your platform's date type if you need to.
pavel_lishin · 2h ago
> The translation from/to this representation to a broken-down y/m/d takes only ~50 lines of code anyways.
Didn't the article explicitly tell us not to write our own date parsing library?
kccqzy · 1h ago
I disagree with that. And furthermore it's not parsing. It's converting between a single integer and a tuple of three integers.
habibur · 2h ago
> or my favorite January 1, 1600 since 1600 is a multiple of 400
You need to deal with 1600 and 2000 being leap year.
While 1700, 1800, 1900 not being a leap year.
I limit dates from 1900 to 2100. All !year%4 = leap year.
Especially when you try to convert int_date to y,m,d things get tricky.
kccqzy · 1h ago
That's exactly why I propose a multiple of 400, not a multiple of 100. The proleptic Gregorian cycle is a 400-year cycle. There are 97 leap years in it. What's tricky about it? Just take a look at my code: https://github.com/kccqzy/smartcal/blob/9cfddf7e85c2c65aa6de...
jerf · 2h ago
"Years are not leap years, unless % 4, unless % 100, unless % 400."
It's a wacky rule for sure.
2000 was fun. Everyone knows about "unless % 4", but there was also an interesting and very vocal set of people who knew about the "unless % 100" but somehow knew that without knowing about the "unless % 400" part. A very specific level of knowledge.
shadowgovt · 1h ago
IIUC why medical cares at all, this is really insightful. Because as far as I'm aware, the medical industry basically uses birthdate as a key; it helps to (a) tell two patients with other primary keys (like name or address) apart and (b) do a quick mental-acuity check on the patient by just having them regurgitate the value and doing a human-brain string= on it.
dlachausse · 3h ago
Even better, just make the user input dates using a calendar date picker widget instead of a text field. This gives you full control of the input.
mattkrause · 3h ago
I always find that a little annoying: it takes way too many clicks (esp. for a birth year) and then you've got to find the day of the week.
I'd hate it less if typing updated the widget.
Tyr42 · 3h ago
I've had to click back once per year old I am sometimes. I'd rather just type my birthday.
takinola · 2h ago
No other programming concept has caused me more grief than dealing with time and timezones. It starts to get really mind-bendingly complex once you start thinking about it deeply. That is even before you start encountering the quirks (some places have timezone changes that depend not only on the time of year but also on the actual year). Lesson learnt - choose a library (moment is great) and never think about time again.
alex_c · 1h ago
Except you do still have to think about time, no matter what… Libraries will help with the really messy details, but even the high level requirements have a lot of pitfalls.
“Simple” example that anyone who’s ever worked on a scheduling application will probably be familiar with:
“Get a list with all of today’s events.”
Well, whose “today” (timezone) are we talking about? Server, client, setting in the user account? Or none of the above, and actually timezone at the physical location of the event, if there is one?
And what does “today” mean, anyway? Truncate the date? 00:00-23:59? Business hours?
And what does “today’s event” even mean? Events can cross midnight… Does an event need to start today? End today? Both? Can events span multiple days?
The fun never ends!
ori_b · 1h ago
Libraries can't paper over the hard parts of dealing with timezones. There are many "right answers" for most date problems. And, they're all what you want for some context. So, the library can't be opinionated about most things.
You just need to understand how time works if you write code handling time.
servercobra · 1h ago
I agree with everything other than "moment is great". Even the devs say don't use it any more, and accidentally mutated datetimes have been the source of bugs in apps I've worked on multiple times. Luxon is great though.
cbm-vic-20 · 1h ago
Unfortunately, not many people in our industry really understand the common pitfalls of timezone management, including the people who set the requirements. The classic "I want this to run at 2am each weekday for the user", and then proceed to simply store that as a UTC offset and call it a day (pun intended).
whatever1 · 1h ago
It’s because it is not systematic historically. It’s a system full of edge cases
hnuser123456 · 1h ago
It's also a beautiful maze of nerd snipes. There's apparently some shifting going on inside the earth, combining with the slight variability of the moon's distance, which means various days over a month can be more than a millisecond shorter than average. Good luck integrating that into your date.addDays()
shadowgovt · 1h ago
The really important thing to remember about timezones is they're not a mathematical construct, or a physics construct, or an astronomy construct... They're a political construct. Framed in that light, they have every bit the complexity of having some piece of your code depend on the law (except it's the law of every nation you expect to be running your code in).
I used to work at a company that stored all dates as ints in a YYYYMMDD format. When I asked why, I was told it was so we could subtract 2 dates to get the difference.
I asked them why they couldn’t use DATEDIFF since this was in a sql db.
They said they hadn’t heard of it and that it must be new.
Do your users type in such dates? No? Problem solved.
The benefit of DIY parsing is to make the problem simple by restricting it to the set of plausible inputs your users will want your code to handle, not to make a highly general library. The right takeaway for juniors is to stop over-complicating things.
colesantiago · 3h ago
I don’t see anything wrong with this. This is actually a fun challenge.
I encourage everyone to learn how to parse the japanese calendar format.
The more people know the better!
jimmaswell · 3h ago
moment is far smaller if you include it without locales you don't need.
I don't care how much they talk themselves down on their homepage, begging me to choose a different library - I like it and I'll continue using it.
> We now generally consider Moment to be a legacy project in maintenance mode. It is not dead, but it is indeed done.
> We will not be adding new features or capabilities.
> We will not be changing Moment's API to be immutable.
> We will not be addressing tree shaking or bundle size issues.
> We will not be making any major changes (no version 3).
> We may choose to not fix bugs or behavioral quirks, especially if they are long-standing known issues.
I consider this a strength, not a weakness. I love a library that's "done" so I can just learn it once and not deal with frivolous breaking changes later. Extra bonus that they plan to continue making appropriate maintenance:
> We will address critical security concerns as they arise.
> We will release data updates for Moment-Timezone following IANA time zone database releases.
TheBigSalad · 2h ago
I couldn't agree more. I have no idea why the moment devs are trying to kill moment.
senfiaj · 3h ago
In UIs prefer date/time pickers instead of raw text inputs which will give the date/time in standard ISO format such as ("2025-07-25" or "2025-07-25T18:47:26.022Z"). Prefer ISO formats everywhere where possible.
somat · 53m ago
The thing that bothers me about the firefox date picker is it display the date in YYYY/DD/MM format.
While I am fairly sure this a a locale defined thing. locales are this huge pile of worms and I have never figured out how to change it to show YYYY-MM-DD format
jedberg · 3h ago
Things you should never do:
Make your own load balancer software
Make firewall software
Make a date parsing library
Attempt to verify an email with a regular expression.
9dev · 2h ago
> Attempt to verify an email with a regular expression.
.+@.+
That one always seemed sufficient for me, every issue after that is the users problem
jedberg · 2h ago
Obviously there is a bit of nuance here, but the best rule of thumb is use a regex and then warn the user that it doesn't look valid but still accept it if it doesn't pass, and then send an email to verify it.
Good general rule of thumb, but desperate scenarios call for desperate measures. I would never do this in Python or Rust for example, but it's necessary in Javascript; `Date` and `Moment`, are so full of traps that the ends justify the means: Especially if you have use for a `Date` or `Time` type.
jimmaswell · 3h ago
moment's given me no trouble at all. I certainly haven't found it to be full of traps. Addressing the most common complaint: a moment object is mutable, sure - that's a valid design choice, not a trap. Follow the docs and everything works perfectly well IME.
the__alchemist · 3h ago
As a specific point, I have not safe found a way to represent a date or time in Moment. When I point this out, I generally get agreement from people who are more used to other languages, and the claim that "You should never be representing a date or time; everything should be a datetime" by JS devs.
But subtle plug of something I made long ago for when you find your data pipelines are running hot parsing timestamp strings etc: https://github.com/williame/TimeMillis
I’m still pumped by the performance of the thing! :)
thangalin · 3h ago
On a slightly related note, here's an algorithm for parsing time from natural inputs into a normalized time:
In 2009 I made a note that Excel's main date parsing function was over 1000 lines of code -- not including helpers.
fitsumbelay · 3h ago
before I even read the post lemme just say "too late, friend. faaaaar too late ..."
aaroninsf · 56m ago
Funny,
I wrote my own, so had to click, but mine was for a very different use case: converting extremely varied date strings into date ranges,
where a significant % of cases are large number are human-entered human-readable date and date range specifiers, as used in periodicals and other material dating back a century or two.
I.e. I had correctly interpret not just ISO dates, but, ambiguous dates and date ranges as accepted in (library catalog) MARC records, which allows uncertain dates such as "[19--]" and "19??", and, natural language descriptors such such as "Winter/Spring 1917" and "Third Quarter '43" and "Easter 2001." In as many languages as possible for the corpus being digitized.
Output was a date range, where precision was converted into range. I'd like to someday enhance things to formalize the distinction between ambiguity and precision, but, that's a someday.
When schema is totally uncontrolled, many cases are ambiguous without other context (e.g. XX-ZZ-YYYY could be month-day-year or day-month-year for a large overlap); and some require fun heuristics (looking up Easter in a given year... but did they mean orthodox or...) and arbitrary standards (when do seasons start? what if a publication is from the southern hemisphere?) and policies for illegal dates (Feburary 29 on non-leap-years being a surprisingly common value)...
In a dull moment I should clean up the project (in Python) and package it for general use...
micromacrofoot · 3h ago
Multiple times in my career I've had a good laugh when a non-technical manager says something along the lines of "it's just the date, how hard can it be?"
indymike · 3h ago
Add phone numbers, email addresses and human names to the list.
peheje · 1h ago
Agreed! My team is constantly humbled by the mess of user data: names, birthdays, addresses, people dying or living abroad etc.
Honestly, sometimes I think about the linear algebra, AI, or robotics I learned in school and get this feeling of, "Is this what I'm doing? Stuff that feels like it should be simple?"
It's funny, even our product manager - who is a great guy - can fall into that "come on, this should be easy" mode, and I'll admit I sometimes get lulled into it too. But to his credit, every time I walk him through the actual edge cases, he totally gets it and admits it's easy to forget the on-the-ground complexity when you're in 'planning mode'.
So yeah, seeing your comment is incredibly validating.
micromacrofoot · 2h ago
What do you mean we shouldn't have a first and last name input?
explains the naming conventions of every culture on the planet
econ · 2h ago
Just validate the registration form? Surely this is a solved problem?
Uhhh...
danesparza · 3h ago
I mean. Yes. Don't write your own date parsing library. Unless you want to go nuts.
So go ahead, write your own date library, your own Unicode font rendering, compiler, OS, game engine or what ever else people tell you to never do because its hard.
Having said that, I don't think date libraries are hard, I think they're messy. Mostly because humans keep introducing convenience fudges - adding a second here, taking eleven days off there, that kind of thing.
The messaging here is that you should be careful about using what you build on your own because it:
- hasn't been battle tested
- likely has bugs
- isn't mature
The only way that it will be all of those things is if someone invests time and energy in them.
From an ecosystem perspective this is absolutely the right thing. You want duplicate projects. You want choice. You want critical knowledge to be spread around.
I see it as “Dont write your own X, unless you want to maintain X. Here be dragons, this problem is deeper than it appears, the first 80% will be easy, the next 15% will annoy you, and the last 5% will consume your life for weeks, months, or even years. Or you could use a library”
The things that people write that everyone uses have had HUGE exposure.
They've been exposed to all the edge cases, they've been tested millions, if not billions of times. All the bugs ironed out.
The people who've worked on them are now the greatest domain experts on that little corner of comp-sci.
Yours won't unless it hits prime time.
So yours will be weak, brittle and dangerous.
The point is, before you release your new thing, make sure it addresses all of the pain points the previous solutions have already slogged through,
or that if it doesn't, people are still aware of when they can arise, and why your thing has chosen not to mitigate them yet,
or ever, if it's an opinionated piece of tech.
My most valuable resource is time. Sure, I could learn more low-level aspects of my craft ... and sometimes I find it useful to do so.
When I focus on doing the hardest, already solved things by re-implementing them my own way, what value am I adding?
I've never met a client who cared about a library or how I did something in code - until it broke. Then, they didn't care who wrote it, they just cared it started working again.
I agree with you though, do the hard things even if it doesn't work 100% right you will have learned a lot. In university I had to implement all of the standard template library data structures and their features, it wasn't as robust as the actual STL but the knowledge of how those work under the covers still comes up in my day to day job.
[0] https://www.space.com/astronomy/earth/earth-will-spin-faster...
Stargate SG-1 is one of my favorite instances of this. The first couple of episodes address the fact that the Earth characters do not speak the same languages as everyone else in the galaxy. Then, having established the point that A: the show runners understand this is an issue and B: it makes for a rather tedious watch, they moved on to "everyone speaks English" and we all breathed a sigh of relief. I just think of it as part of the "camera" now. It turns out that we don't necessarily want a truly literal recording of what such things would look like.
[1]: https://tvtropes.org/pmwiki/pmwiki.php/Main/CallARabbitASmee...
Like, in a story background I'm pushing around, there's a coalition of a large amount of species developed on different planets. And you're a military officer, and you need to coordinate shifts, but - assuming some collectively normalized number of hours - some of your tiny dudes are tuned to 3 hours of sleep, 3 hours of leisure and 3 hours of work, others weird dudes with 2 arms and 2 legs are tuned to 38 hour cycles, and some huge dudes with a trunk in their face are tuned to 356 hour cycles.
Even if you could train and adjust this by an hour or two (which, for the 3 hour dudes would compare to an 8 earth-hour extension of duty for us), how the heck would you coordinate any kind of shifts across this? Or does every species have their own schedule? Good look finding crossover meetings then. Some of the small guys would have to do overtime for longer meetings even.
But you have to make it a point of the story and the challenges if you want to include it. If it is just a weird side note, just say that they figured out a conversion and that's it.
If you’ve read David Weber’s Safehold series, this point gets super clear. It's written with names like "Zherald Ahdymsyn" (Gerald Adamson), but that makes it quite the slog for many.
That doesn't make it unusable as a cross galactic time unit, and I think the same goes for years and hours.
(... it's not exactly pi-squared because the French yanked it around a bit before settling into the modern number based on light in a vacuum and cesium atoms).
https://en.wikipedia.org/wiki/Caesium_standard
I don't think that helps with the original concern.
"Our dates start x trillion rotations of pulsar y ago and our unit is defined as z wiggles of cesium" is a starting point.
But you can tell an alien species our units are expressed in multiples of that, and they can translate it into how theirs works. (Vinge, for example, has space-faring humans talk about "megaseconds" and "gigaseconds" rather than days/years.)
No comments yet
https://babylon5.fandom.com/wiki/Measurements_of_Time
Aliens use phrases like " 2 of your Earth days "
Agree I've never met a farmer who cares about DST. Though also, for non-ag farmers, sometimes "crack of dawn" isn't early enough lol. Cow: "Dairy barn has electric lights, why aren't you awake at 4am tending to my needs, Human? Vacation? Lol no, stay here. Every morning. 4am."
The first is significantly easier as it requires remembering only a single offset and then going with societal conventions.
Likewise Daylight savings is a concept that had its uses, but makes less sense as technology progresses. I don't think even farmers care much about 7AM approximating to sunrise and 6PM as sunset.
Some of the things in the standard are surprising, like maybe were a special request. At the time, I commented, something like, Somewhere, in the French countryside, there is a person who runs an old family vineyard, that is still stamping their barrels with the timepoint information [...]. And that person's lover was on the ISO 8601 committee.
(I once wrote an time library in Scheme that supported everything in ISO 8601. It did parsing, representation, printing, calendar conversion, and arithmetic. Including arithmetic for mixed precision and for relative values. It was an exercise in really solving the problem the first time, for a core library, rather than cascading kludges and API breakage later. I don't recall offhand whether I tried to implement arithmetic between different calendar systems, without converting them to the same system.)
Temporal has other cool types, each with distinct semantics:
- Instant: a fixed point in time with no calendar or location. Think e.g. "the user logged in at X date and time" but valid across the world for any timezone or calendar system. This is what we usually use "Unix UTC timestamps" for.
- ZonedDateTime: like an Instant but associated with a particular calendar and location. Think an Instant but rendered "real" into a calendar system and timezone so the user can see a meaningful time for them.
- PlainDate: already discussed. Think e.g. birthdates.
- PlainTime: think "run task every day at 6:30pm".
- PlainDateTime: like an Instant but associated with a calendar system, but no timezone. Think e.g. what a user would insert in a datetime picker, where the timezone is implied instead of explicitly selected.
- PlainYearMonth: think e.g. "we'll run our reports during October 2025".
- PlainMonthDay: think e.g. "my birthday is June 13".
- Duration: think e.g. "the task ran for 3hrs 30min".
Also see its important concepts[2].
[0] https://tc39.es/proposal-temporal/docs/
[1] https://tc39.es/proposal-temporal/docs/#Temporal-PlainDate
[2] https://tc39.es/proposal-temporal/docs/timezone.html
FHIR in my opinion has a pretty good system for dates (including birthdates): YYYY, YYYY-MM, or YYYY-MM-DD. (Not knowing your exact birthday is common for some countries).
https://build.fhir.org/datatypes.html#date
I faced a similar problem with a form where people were supposed to submit a date and probably not aware of what timezone was involved. I figured that so long as they selected "02/28/1993" and people always saw "02/28/1993" that was correct and if they ever saw it differently it was wrong. So I used non-TZ aware dates throughout the whole system.
Is this DD/MM/YYYY or MM/DD/YYYY? I can tell from the 18 that it's the latter, but that convention isn't universal. I'd recommend YYYY/MM/DD as a less ambiguous format, but I don't have a perfect answer.
https://ijmacd.github.io/rfc3339-iso8601/
https://developer.mozilla.org/en-US/docs/Web/HTML/Reference/...
or a text field with some code that converts vernacular dates to a structured format. I don't think users are going to be too weirded out at seeing "1997-04-15" and will probably learn to use that natively.
The hard part is that a lot of devs aren't aware that there's a standard and that standard is superior to the alternatives.
Strictly, it is the extended form of the ISO 8601 calendar date format. (The basic format has no separators.)
ISO 8601 allows any of its date formats (calendar date, week date, or ordinal date) to be combined with a time representation for a combined date/time representation, it is inaccurate both to call any of the date formats part of the time format, and to call the calendar date format the format that is part of the combined date/time format.
(There's a reason why people who want to refer to a simple and consistent standard tend to choose RFC-3339 over ISO 8601.)
You seem to have a reasonably expedient solution for that problem, but it is surprising to have the combination of things you have to have and things you have to be missing to have that problem in the first place.
That's because the developers use datetimes (aka timestamps) to store a single date. Just pick an arbitrary epoch date (such as January 1, 1900 as used by Excel, or my favorite January 1, 1600 since 1600 is a multiple of 400 making leap year calculations even simpler) and store the number of days elapsed since then. The rules involving leap years are much much simpler than rules involving timezones and timezone databases. The translation from/to this representation to a broken-down y/m/d takes only ~50 lines of code anyways.
Of course if you don't need to do arithmetic on dates, just store three numbers, year, month, and day.
https://en.wikipedia.org/wiki/Julian_day
which are the moral equivalent of Unix timestamps with a different offset and multiplier. These work OK for human history but will break if you go far enough into the past or the future because uncertainty in the earth's rotation adds up over time.
If you don't care about timezones timezones may still care about you, if you want to minimize trouble it makes sense to properly use timezone-aware Zulu (GMT) dates for everything if you can.
In certain cases you might be doing data analysis or building an operational database for throttling access to an API or something and you know there are 16-bits worth of days, hours, 5-minute periods or something it can make sense to work relative to your own epoch.
No comments yet
In this case, I'd suggest storing what you mean (the user wasn't born 9,487 days after Jan 1 1970. They were born Dec 23, 1995.)
Storing the literal units (and ONLY the relevant units), as the parent has, is robust and logically+semantically correct (they could add a translation layer for UX so the user doesn't have to be particular, but that's beside the point). Whether you use a string or a struct or some date-only type is moot, as long as you're literally storing the year, month, and day, and only those three things. You can ephemerally convert it to your platform's date type if you need to.
Didn't the article explicitly tell us not to write our own date parsing library?
You need to deal with 1600 and 2000 being leap year.
While 1700, 1800, 1900 not being a leap year.
I limit dates from 1900 to 2100. All !year%4 = leap year.
Especially when you try to convert int_date to y,m,d things get tricky.
It's a wacky rule for sure.
2000 was fun. Everyone knows about "unless % 4", but there was also an interesting and very vocal set of people who knew about the "unless % 100" but somehow knew that without knowing about the "unless % 400" part. A very specific level of knowledge.
I'd hate it less if typing updated the widget.
“Simple” example that anyone who’s ever worked on a scheduling application will probably be familiar with:
“Get a list with all of today’s events.”
Well, whose “today” (timezone) are we talking about? Server, client, setting in the user account? Or none of the above, and actually timezone at the physical location of the event, if there is one?
And what does “today” mean, anyway? Truncate the date? 00:00-23:59? Business hours?
And what does “today’s event” even mean? Events can cross midnight… Does an event need to start today? End today? Both? Can events span multiple days?
The fun never ends!
You just need to understand how time works if you write code handling time.
I asked them why they couldn’t use DATEDIFF since this was in a sql db.
They said they hadn’t heard of it and that it must be new.
2025-01-01 - 2024-12-31 = 20250101 - 20241231 = 8870
i.e. 90 months and 10 days
or 7 years 6 months and 10 days
How is that the same thing as one day?
When is 30 days after today? 25206+30
https://learn.microsoft.com/en-us/dotnet/api/system.globaliz...
https://learn.microsoft.com/en-us/windows/apps/design/global...
The benefit of DIY parsing is to make the problem simple by restricting it to the set of plausible inputs your users will want your code to handle, not to make a highly general library. The right takeaway for juniors is to stop over-complicating things.
I encourage everyone to learn how to parse the japanese calendar format.
The more people know the better!
I don't care how much they talk themselves down on their homepage, begging me to choose a different library - I like it and I'll continue using it.
> We now generally consider Moment to be a legacy project in maintenance mode. It is not dead, but it is indeed done.
> We will not be adding new features or capabilities.
> We will not be changing Moment's API to be immutable.
> We will not be addressing tree shaking or bundle size issues.
> We will not be making any major changes (no version 3).
> We may choose to not fix bugs or behavioral quirks, especially if they are long-standing known issues.
I consider this a strength, not a weakness. I love a library that's "done" so I can just learn it once and not deal with frivolous breaking changes later. Extra bonus that they plan to continue making appropriate maintenance:
> We will address critical security concerns as they arise.
> We will release data updates for Moment-Timezone following IANA time zone database releases.
While I am fairly sure this a a locale defined thing. locales are this huge pile of worms and I have never figured out how to change it to show YYYY-MM-DD format
Make your own load balancer software
Make firewall software
Make a date parsing library
Attempt to verify an email with a regular expression.
Accept people's names
Anything
But subtle plug of something I made long ago for when you find your data pipelines are running hot parsing timestamp strings etc: https://github.com/williame/TimeMillis
I’m still pumped by the performance of the thing! :)
https://stackoverflow.com/a/49185071/59087
I wrote my own, so had to click, but mine was for a very different use case: converting extremely varied date strings into date ranges,
where a significant % of cases are large number are human-entered human-readable date and date range specifiers, as used in periodicals and other material dating back a century or two.
I.e. I had correctly interpret not just ISO dates, but, ambiguous dates and date ranges as accepted in (library catalog) MARC records, which allows uncertain dates such as "[19--]" and "19??", and, natural language descriptors such such as "Winter/Spring 1917" and "Third Quarter '43" and "Easter 2001." In as many languages as possible for the corpus being digitized.
Output was a date range, where precision was converted into range. I'd like to someday enhance things to formalize the distinction between ambiguity and precision, but, that's a someday.
When schema is totally uncontrolled, many cases are ambiguous without other context (e.g. XX-ZZ-YYYY could be month-day-year or day-month-year for a large overlap); and some require fun heuristics (looking up Easter in a given year... but did they mean orthodox or...) and arbitrary standards (when do seasons start? what if a publication is from the southern hemisphere?) and policies for illegal dates (Feburary 29 on non-leap-years being a surprisingly common value)...
In a dull moment I should clean up the project (in Python) and package it for general use...
Honestly, sometimes I think about the linear algebra, AI, or robotics I learned in school and get this feeling of, "Is this what I'm doing? Stuff that feels like it should be simple?"
It's funny, even our product manager - who is a great guy - can fall into that "come on, this should be easy" mode, and I'll admit I sometimes get lulled into it too. But to his credit, every time I walk him through the actual edge cases, he totally gets it and admits it's easy to forget the on-the-ground complexity when you're in 'planning mode'.
So yeah, seeing your comment is incredibly validating.
explains the naming conventions of every culture on the planet
Uhhh...
https://gist.github.com/timvisee/fcda9bbdff88d45cc9061606b4b...