impl Arbitrary for SystemTime #178
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caspermeijn
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| fn arbitrary(u: &mut Unstructured<'a>) -> Result<Self> { | ||
| // Create a SystemTime by adding or subtracting a duration from epoch. | ||
| // The result is not guaranteed to fit. Keep trying until a good SystemTime if found. | ||
| loop { |
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It seems unfortunate to have behaviour of this that is dependent on the target, but since the underlying type requires it, why not #[cfg] or even just check at runtime if the platform considers UNIX_EPOCH the minimal representable timestamp and just not bother with the add/sub on those targets?
Would save on the input bytes and such.
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The docs for SystemTime don't guarantee anything regarding what fits in a SystemTime. So I would not know what to check for. Maybe UNIX_EPOCH is the minimum. Maybe the year 0 is the minimum.
Also, the maximum is interesting. It is not guaranteed that SystemTime::UNIX_EPOCH + Duration::MAX will fit. Therefore, it needs to be checked.
I could determine the minimum and maximum by trail and error, save this result and use that to make sure we never generate a value that doesn't fit. But that isn't great code as well.
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UNIX_EPOCH.checked_sub(Duration::from_nanos(1)).is_none() implies that UNIX_EPOCH is the min value representable. This could be checked once and saved in a static or somesuch.
Unfortunately I've no good ideas for the maximum, so yeah, you would need the loop regardless. Feel free to ignore the comment until others chime in.
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As I understand, the minimum and maximum are platform-specific. I see three possible solutions:
- Try to generate a value, check whether in range, if not, loop (current patch)
- Try to find min and max, save those values, then generate a value in between (thus moving the loop to the process of finding the min and max)
- Work with upstream to define the min and max as a constant (Duration has a min/max, so why shouldn't SystemTime)
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