Short Duration constants

[joshtriplett]

Proposal

Problem statement

A comment on rust-lang/rust#57391 suggested this, and I thought it would be a great idea:

We have Duration::MILLISECOND, Duration::MICROSECOND, and Duration::NANOSECOND. These are very long names, for a concept that's usually written abbreviated.

I'd propose that we additionally add Duration::MS, Duration::US, and Duration::NS, with the same values.

Motivating examples or use cases

As with the existing constants:

time::sleep(Duration::MS);
let timeout_time = my_event.arrived_at + 100 * Duration::US;

Solution sketch

impl Duration {
    pub const MS: Duration = Duration::from_millis(1);
    pub const US: Duration = Duration::from_micros(1);
    pub const NS: Duration = Duration::from_nanos(1);
}

Alternatives

Instead of MS/US/NS, we could use MILLI/MICRO/NANO.

Links and related work

rust-lang/rust#57391

What happens now?

This issue contains an API change proposal (or ACP) and is part of the libs-api team feature lifecycle. Once this issue is filed, the libs-api team will review open proposals as capability becomes available. Current response times do not have a clear estimate, but may be up to several months.

Possible responses

The libs team may respond in various different ways. First, the team will consider the problem (this doesn't require any concrete solution or alternatives to have been proposed):

• We think this problem seems worth solving, and the standard library might be the right place to solve it.
• We think that this probably doesn't belong in the standard library.

Second, if there's a concrete solution:

• We think this specific solution looks roughly right, approved, you or someone else should implement this. (Further review will still happen on the subsequent implementation PR.)
• We're not sure this is the right solution, and the alternatives or other materials don't give us enough information to be sure about that. Here are some questions we have that aren't answered, or rough ideas about alternatives we'd want to see discussed.

[the8472]

Duration::US

😬

I'd rather use µs, and silence the warnings than THAT.

[kennytm]

I'd rather use µs, and silence the warnings than THAT.

Constants are supposed to be upper case, which would become ΜS (greek letter mu) and is confusable with MS (latin letter m).

---

Actually would naming them MILLIS, MICROS, NANOS be an acceptable compromise? At least they are consistent with existing names like from_millis.

Edit: found that it was already proposed before as Duration::{SEC, MILLI, MICRO, NANO} in the previous FCP attempt back in 2019 rust-lang/rust#57391 (comment), turns out a bit controversial though, 👍3 👎2.

[kennytm]

I'd propose that we additionally add Duration::MS, Duration::US, and Duration::NS, with the same values.

Since rust-lang/rust#57391 is still unstable I'd propose we either keep the long name only, or replace them with the short name, instead of having both sets.

[cuviper]

Constants are supposed to be upper case, which would become ΜS (greek letter mu) and is confusable with MS (latin letter m).

Good thing megaseconds are uncommon...

[tgross35]

Constants are supposed to be upper case, which would become ΜS (greek letter mu) and is confusable with MS (latin letter m).

Good thing megaseconds are uncommon...

You mean megasiemens? 🙃 (which are actually common, at least in my world...)

[the8472]

Constants are supposed to be upper case

"supposed to" is just a guideline and causes more problems than good here, which is why I said I would silence the warnings (capitalization + rare codepoints) than following the convention.

[Skgland]

silence the warnings (capitalization + rare codepoints) than following the convention.

Unfortunately the uncommon_codepoints lint can only be disabled at the crate level and doesn't work on individual items rust-lang/rust#86824

[pitaj]

Am alternate proposal: std::time::units

API

// in std::time

mod units {
    #![allow(non_upper_case_globals)]

    use super::Duration;

    pub const sec: Duration = Duration::SECOND;
    pub const ms: Duration = Duration::MILLISECOND;
    pub const us: Duration = Duration::MICROSECOND;
    pub const ns: Duration = Duration::NANOSECOND;
}

Usage:

use std::time::units::*;

let delay = 25 * ms;

[shepmaster]

It's a shame you can't import-rename an associated constant. If you could, then users could do this themselves:

use std::time::Duration::MILLISECOND as ms;
let delay = 25 * ms;

The current error

error[E0432]: unresolved import `std::time::Duration`
 --> src/main.rs:3:20
  |
3 |     use std::time::Duration::MILLISECOND as ms;
  |                    ^^^^^^^^ `Duration` is a struct, not a module

[ChrisDenton]

It's a shame you can't import-rename an associated constant.

That was briefly discussed in the libs meeting. It is a desirable feature but it's not likely to arrive anytime soon.

[cuviper]

It is mostly equivalent for a user to define a new constant:

const ms: Duration = Duration::MILLISECOND;

I think documentation might be the only practical difference?

[programmerjake]

if you're going to have units::us, you could also then have units::μs (using the greek letter rather than \u{B5} since the greek letter is preferred according to section 2.5 of https://www.unicode.org/reports/tr25/)

[the8472]

I have doubts about the consortium's recommendation. some international keyboard layouts have a dedicated key-combo for that and that produces \u{B5}, and one of the reasons why sigils are chosen is the ability to type them.... we're not scalaz