add isless method for FixedTimeZone #491
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| Defines a true chronological ordering for FixedTimeZone objects, answering | ||
| the question: "which time zone represents an earlier moment in absolute time?" | ||
| The core principle is that a time zone is "chronologically earlier" (less than) | ||
| if its numerical UTC offset is "mathematically greater". |
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The ordering of a FixedTimeZone vs. a FixedTimeZone could definitely work either way and I don't think it should be relied upon for performing chronological sorting of time instants.
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Without this definition the comparison would define "UTC-5" as less than "UTC-4" since it is numerically smaller.
julia> FixedTimeZone("UTC-5").offset.std
-18000 seconds
julia> FixedTimeZone("UTC-4").offset.std
-14400 secondsThere was a problem hiding this comment.
I agree there should be an ordering but I'm not sure on what the ordering should be. I would expect most users would expect the most negative offset to be first in the list. However, that is chronologically backwards:
julia> using TimeZones
julia> tzs = [tz"UTC-4", tz"UTC+1", tz"UTC-5"]
3-element Vector{FixedTimeZone}:
UTC-04:00
UTC+01:00
UTC-05:00
julia> sort!(ZonedDateTime.(2025,6,17,tzs))
3-element Vector{ZonedDateTime}:
2025-06-17T00:00:00+01:00
2025-06-17T00:00:00-04:00
2025-06-17T00:00:00-05:00
julia> Base.isless(a::FixedTimeZone, b::FixedTimeZone) = isless(a.offset, b.offset)
julia> sort!(tzs)
3-element Vector{FixedTimeZone}:
UTC-05:00
UTC-04:00
UTC+01:00
julia> Base.isless(a::FixedTimeZone, b::FixedTimeZone) = isless(b.offset, a.offset)
julia> sort!(tzs)
3-element Vector{FixedTimeZone}:
UTC+01:00
UTC-04:00
UTC-05:00Maybe the compromise is to define a is_chrono_less(::FixedTimeZone, ::FixedTimeZone)? That way downstream dependents can have a guaranteed ordering
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Yeah, I agree this can break downstream, I don't think this PR is needed anymore, I'll do the comparison on the offset isless(y.offset, x.offset)
add suggestions Co-authored-by: Curtis Vogt <[email protected]>
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Closing as this PR is not longer needed. |
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Description
This PR adds support to sort FixedTimeZones by adding a comparison method isless.