Instant is monotonically nondecreasing #43756
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We don't want to guarantee that `Instant::now() != Instant::now()` is always true since that depends on the speed of the processor and the resolution of the clock.
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r? @brson (rust_highfive has picked a reviewer for you, use r? to override) |
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Mathematically speaking, "monotonically increasing" already means x ≥ y ⇒ f(x) ≥ f(y), what you are thinking is "strictly increasing". |
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@kennytm actually "strictly increasing" is: "Monotonically increasing" (or "nondecreasing") however is: |
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@scalexm Thanks, updated the arrow. |
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Ah right - I think only the second fix is needed then. |
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Er, actually, I think the first change is still correct - Wolfram defines "monotonic function" as "A monotonic function is a function which is either entirely nonincreasing or nondecreasing." (http://mathworld.wolfram.com/MonotonicFunction.html), so Instant is monotonic, but not monotonically increasing, which is defined as "Always increasing; never remaining constant or decreasing." (http://mathworld.wolfram.com/MonotoneIncreasing.html) |
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@sfackler From my understanding of english terminology, "monotonically increasing" or simply "increasing" usually means "strictly increasing", but sometimes it can just mean "nondecreasing", depending on authors and contexts. So I think you should indeed stick with "monotonically nondecreasing" which is unambiguous. But anyway the second fix is the most important since "greater" indeed means "strictly greater" with standard terminology. |
src/libstd/time/mod.rs
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| /// Opaque and useful only with `Duration`. | ||
| /// | ||
| /// Instants are always guaranteed to be greater than any previously measured | ||
| /// Instants are always guaranteed to no less than any previously measured |
aidanhs
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@bors: r+ rollup |
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📌 Commit 97d046a has been approved by |
…lexcrichton Instant is monotonically nondecreasing We don't want to guarantee that `Instant::now() != Instant::now()` is always true since that depends on the speed of the processor and the resolution of the clock.
We don't want to guarantee that
Instant::now() != Instant::now()isalways true since that depends on the speed of the processor and the
resolution of the clock.