I've seen this question asked before but I don't think I've seen an official answer. Is it intended ...

# kotlinx-datetime

[russhwolf]

I've seen this question asked before but I don't think I've seen an official answer. Is it intended that TimeZone.UTC is not equivalent to TimeZone.of("UTC")? That's incredibly unintuitive.

[kevin.cianfarini]

Mind upvoting this issue? https://github.com/Kotlin/kotlinx-datetime/issues/222

[russhwolf]

That issue is confusing to me as written. I don't think the root issue is the serialization. I think the issue is that the object returned by TimeZone.of("UTC") is not equal to TimeZone.UTC.

[russhwolf]

The root cause is presumably the same, but I don't think that ticket communicates well why it's so confusing

[kevin.cianfarini]

Drop a comment that adds to this, then? Someone else mentions later down in the thread that .of("UTC") and .UTC are not equal.

[kevin.cianfarini]

But, for what it's worth, I agree. It's incredibly confusing and surprising behavior.

[kevin.cianfarini]

And I still don't see the use case for FixedOffsetTimeZone that UtcOffset doesn't cover 🙃

[russhwolf]

I logged https://github.com/Kotlin/kotlinx-datetime/issues/474 and left a comment that they're related

[Daniel Pitts]

Looking at the source, it appears that .of("Z") will be the same as .UTC, but GMT/UTC/UT are handled differently:

if (zoneId == "UTC" || zoneId == "GMT" || zoneId == "UT") {
                    return FixedOffsetTimeZone(UtcOffset.ZERO, zoneId)
                }

[Daniel Pitts]

Also looking at the source, it looks like the equals operator doesn't take into account the Z vs UTC being equivalent:

actual override fun equals(other: Any?): Boolean =
        this === other || other is TimeZone && this.id == other.id

    override fun hashCode(): Int = id.hashCode()

[Daniel Pitts]

Further investigation, it looks like the UtcOffset class on the JVM has this:

public actual val ZERO: UtcOffset = UtcOffset(ZoneOffset.UTC)

and

actual override fun toString(): String = zoneOffset.toString()

ZoneOffset is a Java class, and its toString will return Z for the zero offset, or will return the [-|+]hh:mm:ss (optional seconds) based on the offset.

[kevin.cianfarini]

I commented on one of the issues I’ve filed and figured it might be good to drop here. There’s currently three Github issues which touch on this confusion.

https://github.com/Kotlin/kotlinx-datetime/issues/222#issuecomment-2619294021