Add const fn none()

[dhardy]

Both Duration and Instant are explicitly optional types, so why not add this?

Alternative: add NONE as an associated constant. Simpler, but less flexible in case the internal representation changes.

Workaround: both support From<Option<..>> already.

[dhardy]

Related questions:

• Should Instant::default() return a "none" value? This is the only sensible value it could return; whether it should depends on the point of view: is "none" an error state or is the type explicitly optional?
• Should Duration::default() return "none" instead of "zero"?
• (Is there even a good reason to have your own Duration type here instead of just returning Option<Duration> from Instant::duration_since?)

My motivation: what I actually want is to represent the last time something happened, if any. Option<Instant> works, but is clunky enough that I was going to write my own wrapper, before discovering you basically did that. Panic-free operations is just a bonus from my point of view.

[taiki-e]

Thanks! Seems reasonable to have such a feature.

Alternative: add NONE as an associated constant.

Given that these types already have some associated constants, associated constants may be more consistent. That said, I have no strong opinion on this.

Simpler, but less flexible in case the internal representation changes.

It is interesting that associated constants are less flexible than const fns, but I'm not too worried about this as we can define an associated constant using a private const fn.

• Should Instant::default() return a "none" value? This is the only sensible value it could return; whether it should depends on the point of view: is "none" an error state or is the type explicitly optional?
• Should Duration::default() return "none" instead of "zero"?

The first purpose of this crate was to use None as an error state, so I think using None as some form of default can be a pitfall for those who use this crate for that purpose.

• (Is there even a good reason to have your own Duration type here instead of just returning Option<Duration> from Instant::duration_since?)

Sorry, I'm not sure what you mean. The current easytime::Instant::duration_since's signature is equivalent to std.

[dhardy]

The first purpose of this crate was to use None as an error state, so I think using None as some form of default can be a pitfall for those who use this crate for that purpose.

Both types have an is_none() method, not an is_err() method, which doesn't lead to that assumption.

But in that case, I guess this crate is redundant since rust-lang/rust#89926 ?

[taiki-e]

dtolnay/request-for-implementation#27 and rust-lang/rust#58395 are the context of this crate.

I agree that none does not necessarily mean err, as it is up to the user to decide how to handle the results, but this crate was originally created with the use case of treating none as effectively err in mind.

(EDIT: To clarify, I'm not negative at all about the other use cases. I'm just concerned about a potential pitfall of the API for known use cases.)

But in that case, I guess this crate is redundant since rust-lang/rust#89926 ?

Well, that PR fixes the most annoying problem, but they are not the only operations that cause panic.

[dhardy]

Updated. I probably won't end up using this library myself, so leave it to you to decide what to do with this.

[taiki-e]

bors r+

[bors]

Build succeeded:

• ci

[taiki-e]

Published in 0.2.3.