Nodatime BclDateTimeZone EqualsImpl throws NotImplementedException
The method EqualsImpl
in the Nodatime class BclDateTimeZone
calls a NotImplementedException
. It is documented to behave this way - is there a reason for this?
If the equality test is two ZonedDateTime
that use BclDateTimeZone
, this throws an exception.
Is this a bug, doesn't it feel right?
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It is documented to behave this way - is there a reason for this?
Yup - it is generally very difficult to determine the equality of the zone in general terms. Suppose we have two instances BclDateTimeZone
that carry two different values TimeZoneInfo
... we could:
- They are said to be not arbitrarily equal, even if they are logically equivalent
- Compare them by ID (not possible in PCL, which does not support IDs, and is split into Mono, why
TimeZoneInfo.Local
hasLocal
IIRC ID ) - Compare them for equality through history, which is very expensive.
I agree that this is a pain, and I think I plan to remove value equality ZonedDateTime
entirely in Noda Time 2.0 and make ZonedDateTime
use of reference equality.
If you want to compare time zones, a better alternative would probably be to use ZonedEqualityComparer
to indicate how you want them to be compared.
But the inability to compare values ZonedDateTime
for equality when using BCL values is definitely nasty. I raised a bug ; I am preparing version 1.3.1 and I can check if I can fix it instead of waiting for 2.0.
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After trying to enter failed unit tests to prove this error, I found it difficult to reproduce.
Comparing ZonedDateTime
with BclDateTimeZone
at different offsets is not a problem. Comparison ZonedDateTime
with different is LocalDateTime
not a problem.
I could see from the source that comparison ZonedDateTime
Zone
only comes into play if the tags LocalDateTime
and Offset
are equal.
My problem came when I was using two different references BclDateTimeZone
at the same offset. I did it using DateTimeZoneProviders.Bcl.GetSystemDefault()
one place and BclDateTimeZone.ForSystemDefault()
another. Needless to say, they now call common code.
I have this failed test where I am comparing two ZonedDateTime
with different ones DateTimeZone
at the same offset:
ZonedDateTime dtzOne = new ZonedDateTime(Instant.FromUtc(2014, 11, 11, 21, 00), DateTimeZoneProviders.Bcl.GetZoneOrNull("Greenwich Standard Time"));
ZonedDateTime dtzTwo = new ZonedDateTime(Instant.FromUtc(2014, 11, 11, 21, 00), DateTimeZoneProviders.Bcl.GetZoneOrNull("GMT Standard Time"));
Assert.That(dtzOne, Is.Not.EqualTo(dtzTwo));
This test throws an exception:
System.NotImplementedException : The method or operation is not implemented.
at NodaTime.TimeZones.BclDateTimeZone.EqualsImpl(DateTimeZone zone)
at NodaTime.DateTimeZone.Equals(DateTimeZone obj)
at NodaTime.ZonedDateTime.Equals(ZonedDateTime other)
I can work around this problem easily, but it is probably worth fixing.
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