As the author of Jiff, I don’t like it either. But I didn’t see any other feasible way to improve Rust’s datetime offering. (The sibling comment links to a more in depth answer.)

It would be better if there was one datetime library. It would be better if chrono had just been done “right” from the start. But it wasn’t. So I can either go to the chrono maintainers and say, “please let me, a non-expert in datetimes, have full creative control over the project” or I can go build something on my own and, in the process, become an expert. Otherwise, we stay stuck in our local optimum.

As a fan of xkcd, this is probably least favorite xkcd. On the one hand, yes, it aptly expresses frustration. On the other, it’s easy to use as a club against progress itself. Sometimes you need to start fresh to move the needle. Rust is a perfect example of that itself.

Yeah this is a tough one. I’m not sure the right thing to do is for me to go around blasting PRs at those projects. They’re probably already carrying support for both chrono and time, and asking them to support a third that is brand new is a bit of a stretch I think. Especially since I’ve promised breaking changes in the not-too-distant future. (Although I would like to do a Jiff 1.0 release about 1 year from now and commit to stability.) At least, I know I’d be hesitant if I were on the other side of it. But maybe folks are more flexible than me, I’m not sure.

I’ve been noodling on just adding these integrations to jiff itself. I do worry that if I do that, then the integrations will always stay with Jiff, even at 1.0. But maybe there just isn’t another feasible choice.

But, why do you mention humantime? humantime doesn’t have any integrations with time or chrono. humantime is more like a thin wrapper on top of std::time::Duration and std::time::SystemTime to make parsing and printing a bit nicer.

You should absolutely not need to handle ISO 8601 and RFC 3339 manually. They are supported via the Display and FromStr trait implementations on every main type in Jiff (Span, Zoned, Timestamp, civil::DateTime, civil::Date and civil::Time). It’s technically an implementation of a mixture of ISO 8601, RFC 3339 and RFC 9557, but the grammar is specified precisely by Temporal. See: https://docs.rs/jiff/latest/jiff/fmt/temporal/index.html

OK, I’ve beefed that example up a little bit: https://github.com/BurntSushi/jiff/commit/08dfdde204c739e38147faf70b648e2d417d1c2e

I think the comparison is a bit more muddied now and probably worse overall to be honest. Maybe removing DateTime<Local> is the right thing to do. I’ll think on it.

It’s a subtle comparison to make… Probably most people don’t even realize that they’re doing the wrong thing.

OK, fair enough. What should it say instead? Just omit the mention of DateTime<Local>? I used it because it’s literally the only way to derive(Deserialize) in Chrono in a way that gives you DST aware arithmetic on the result without getting time zone information via some out-of-band mechanism.

Again, to be clear, I’m not saying it’s impossible to do. But in order to do it, you have to build your own abstractions. And even then, you still can’t do it because tzfile doesn’t give you enough to do it. And tzfile has a platform specific API with no caching, so every time you parse a datetime with a tz ID in it, it’s completely reloading the TZif data from disk.

Some of these things are implementation quality issues that can be fixed. Others are library design problems where you can achieve your objective by building your own abstractions. Like do you really not see this as something that shouldn’t be mentioned in a comparison between these crates? You must recognize the difference between what you’re doing and just plopping a Zoned in your struct, deriving Serialize and Deserialize, and then just letting the library do the right thing for you. And that mentioning this is appropriate in the context of the “facts of comparison” because it translates into a real user experience difference for callers.

Time zone transition changes happen all the time. Once you start storing datetimes in the future, you’re in a bit of a precarious position here. Moreover, this is a standardized interchange format that other libraries will know how to read/write. (It’s relatively newly standardized, but has been used in practice among other datetime libraries.)

I think you also glossed over some of my other points. How do you write your serialization code using Chrono? Does it work with both chrono-tz and tzfile?

The point is almost never about “it is literally impossible to accomplish task foo,” but rather, it matters how it’s approach and how easy it is to do. And if you have to rely on your users having very specific domain knowledge about this, it’s likely there will be errors. As my design docs state, I didn’t only make Jiff to offer more functionality. I also made it because I felt like the APIs could be better. That’s a very subjective valuation, and I find arguments of the type, “well I can just use the old library in this way as long as I hold it right and it actually works just fine” to be missing the forest for the trees.

The original name I wanted was gigawatt or some variation there of. :)

It’s not built-in support.

Right. That’s exactly what the code snippet says:

    // The serialized datetime has no time zone information,
    // so unless there is some out-of-band information saying
    // what its time zone is, we're forced to use a fixed offset:

So I feel like the point you’re making here is already covered by the example comparison I wrote. It’s not built-in, so you have to invent your own interchange format. And since your serialized format doesn’t include offset information at the time the instant was created, it’s impossible to do offset conflict resolution. For example, let’s say you record one year from today in Ukraine:

use jiff::{ToSpan, Unit, Zoned};

fn main() -> anyhow::Result<()> {
    let now = Zoned::now().round(Unit::Minute)?.intz("Europe/Kyiv")?;
    let next_year = now.checked_add(1.year())?;
    println!("{next_year}");
    Ok(())
}

And the output:

$ cargo -q r
2025-07-22T17:23:00+03:00[Europe/Kyiv]

And maybe you store this datetime somewhere.

At this point, it’s looking like Ukraine is going to abolish DST for next year. So what happens to that datetime above? It no longer has the right offset. So now you need to choose whether to reject it altogether (the default), respect the offset (even if the civil time changes) or respect the civil time (even if the instant changes).

Here’s an example of when this happened with Brazil abolishing DST: https://docs.rs/jiff/latest/jiff/fmt/temporal/struct.DateTimeParser.html#example-3

Is the cache invalidated if system tzdata is updated?

Yes, although at present, there is a TTL. So an update may take “time” to propagate. jiff::tz::db().reset() will force the cache to be invalidated. I expect the cache invalidation logic to get tweaked as we get real experience with it.

And what effect does the answer have on the example from “Jiff supports detecting time zone offset conflicts” if both zoned datetimes used the system timezone which got updated between 1. opening 2. parsing the two zoned datetimes.

It’s hard to know precisely what you mean. But once you get a jiff::tz::TimeZone, that value is immutable: https://docs.rs/jiff/latest/jiff/tz/struct.TimeZone.html#a-timezone-is-immutable

New updates to tzdb are only observed when you do a tzdb lookup.

In this section, wouldn’t be more realistic for chrono users to use timezone info around the wire instead of on the wire, rather than using Local+FixedOffset?

That’s kinda my point. How do they do that? And does it work with chrono-tz and tzfile? And what happens if tzdb updates lead to a serialized datetime with an incorrect offset in a future update of tzdb? There are all sorts of points of failure here that Jiff will handle for you by virtue of tighter integration with tzdb as a first class concept.

How are you doing a date/time library without platform dependencies like libc or windows-sys? Are you rolling your own bindings in order to get the local time zone? (Or perhaps you aren’t doing that at all.)

Ah gotya, thanks!

Disclosure: I’m the author of the memchr crate.

You mention the memchr crate, but you don’t seem to have benchmarked it. Instead, you benchmarked the needle crate (last updated 7 years ago). Can you explain a bit more about your methodology?

The memchr crate in particular doesn’t just use Rabin-Karp. It also uses Two-Way. And SIMD (with support for x86-64, aarch64 and wasm32).

Cross-posting from reddit:

The PR has more details, but here are a few ad hoc benchmarks using ripgrep on my M2 mac mini while searching a 5.5GB file.

This one is just a case insensitive search. A case insensitive regex expands to something like (ignoring Unicode) [Ss][Hh][Ee][Rr]..., which means that it has multiple literal prefixes. In fact, you can enumerate them! As long as the set is small enough, this is something that the new SIMD acceleration on aarch64 can handle (and has done for a long time on x86-64):

$ time rg-before-teddy-aarch64 -i -c 'Sherlock Holmes' OpenSubtitles2018.half.en
3055

real    8.208
user    7.731
sys     0.467
maxmem  5600 MB
faults  191

$ time rg-after-teddy-aarch64 -i -c 'Sherlock Holmes' OpenSubtitles2018.half.en
3055

real    1.137
user    0.695
sys     0.430
maxmem  5904 MB
faults  203

And of course, using multiple literals explicitly also uses this optimization:

$ time rg-before-teddy-aarch64 -c 'Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty' OpenSubtitles2018.half.en
3804

real    9.055
user    8.580
sys     0.474
maxmem  4912 MB
faults  11

$ time rg-after-teddy-aarch64 -c 'Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty' OpenSubtitles2018.half.en
3804

real    1.121
user    0.697
sys     0.422
maxmem  4832 MB
faults  11

And it doesn’t just work for prefixes, it also works for inner literals too:

$ time rg-before-teddy-aarch64 -c '\w+\s+(Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty)\s+\w+' OpenSubtitles2018.half.en
773

real    9.065
user    8.586
sys     0.477
maxmem  6384 MB
faults  11

$ time rg-after-teddy-aarch64 -c '\w+\s+(Sherlock Holmes|John Watson|Irene Adler|Inspector Lestrade|Professor Moriarty)\s+\w+' OpenSubtitles2018.half.en

773

real    1.124
user    0.702
sys     0.421
maxmem  6784 MB
faults  11

If you’re curious about how the SIMD stuff works, you can read my description of Teddy here. I ported this algorithm out of the Hyperscan project several years ago, and it has been one of the killer ingredients for making ripgrep fast in a lot of common cases. But it only worked on x86-64. With the rise and popularity of aarch64 and Apple silicon, I was motivated to port it over. I just recently finished analogous work for the memchr crate as well.

Shortly after we resigned, the top-level team leads, project directors to the Foundation, core team members and the new mods got together to form an interim leadership cohort. Sometimes called the “leadership chat.” That then evolved into the Leadership Council by way of an RFC on goverance.