Add checked operation methods to Duration

[eugene-bulkin]

Addresses #35774.

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[sfackler]

Can we update the Add, Sub etc impls to call into these methods to avoid code duplication?

[nagisa]

Checked duration multiplication

[eugene-bulkin]

Fixed, thanks!

[eugene-bulkin]

@sfackler What's the best way to do that? Only catch I can see is checked_op can fail in a variety of different ways but returns None every time, so there's no way to know exactly why it failed, while the trait impls will panic with the actual error reason.

Edit: To clarify, my question is specifically: do we care about the expect messages we have in there currently? Since a test explicitly checks that overflowing subtraction panics, it appears that the API does want panics for failures.

[sfackler]

It looks like they only fail due to overflow, so you should just be able to do something like

fn add(self, other: Duration) -> Duration {
    self.checked_add(other).expect("overflow when adding durations")
}

[eugene-bulkin]

So how about this:

• add has the expect message "overflow when adding durations"
• sub has the expect message "overflow when subtracting durations"
• mul has the expect message "overflow when multiplying duration by scalar"
• div has the expect message "divide by zero error when dividing duration by scalar"

Are those reasonable? Or are the last two too wordy?

[sfackler]

Those all seem reasonable. I wouldn't worry too much about the wordyness - people hopefully shouldn't be seeing them very often :)

[eugene-bulkin]

Looks like doc-tests are failing. I'll get those fixed ASAP.

[alexcrichton]

Looks good to me! r=me when the tests are passing

[eugene-bulkin]

Doc-tests failing now because I marked the functions as unstable.

Should I leave the marked as unstable and add the #![feature(duration_checked_ops)] part in the attributes? Or should I mark them as stable?

[sfackler]

You should add the attributes in the examples.

[alexcrichton]

@bors: r+

Thanks!

[bors]

📌 Commit b6321bd has been approved by alexcrichton