Document various trait invariants / requirements #516
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bkirwi
commented
Mar 17, 2023
| @@ -28,14 +31,21 @@ pub trait PathSummary<T> : Clone+'static+Eq+PartialOrder+Debug+Default { | |||
| /// in computation, uses this method and will drop messages with timestamps that when advanced | |||
| /// result in `None`. Ideally, all other timestamp manipulation should behave similarly. | |||
| /// | |||
| /// This summary's partial order is expected to be compatible with the partial order of [T], | |||
| /// in the sense that if `s1.less_equal(s2)`, then `s1.results_in(&t)` is less than or equal to | |||
| /// `s2.results_in(&t)`. | |||
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It seems clear that we do assume roughly that the smallest summary advances the timestamp the least, but I'm not confident I have this description exactly right.
| /// `s2.results_in(&t)`. | ||
| /// | ||
| /// Note that `Self::default()` is expected to behave as an "empty" or "noop" summary, such that | ||
| /// `Self::default().results_in(&t) == Some(t)`. |
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Cycle checking seems to assume that non-default summaries always advance the timestamp. Is that a requirement?
At time of writing, I'm not sure about the exact relationship here, but there definitely ought to be one!
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Some of these I have picked up in conversation; others come from documenting what the code seems to assume. Happy to be corrected if I got something wrong!