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kotlinlang

QQ: If I am a library author, can I update the library's kotlin version without requiring its consumers to update as well? Specifically 1.3.72 -&gt; 1.4.0

If you want to use 1.4.0 stdlib features, you can't - your consumers will need the new library or crash. If you want to just use 1.4 language features, I think you could stay on 1.3 and tell the compiler to use language level 1.4.

how do you tell the compiler to use language level 1.4?

How do I stay on 1.3 and ask compiler to use 1.4? I just want trailing commas tbh in my libraries. Nothing I need from 1.4 stdlib (for now)

You can update the Kotlin compiler to 1.4, and pass `-api-version 1.3`. This will allow you to use new language features, but not the new API. It’s called `apiVersion` in Gradle, I think

Sweet. I'm on maven (for reasons), so I'll just add a prop. Found this: <https://kotlinlang.org/docs/reference/using-maven.html>

Sidenote: This still lists 1.4 as experimental

language version would still be 1.4 (or unspecified, right?)

Yes, language version defaults to the compiler version, if not specified

Seems like `apiVersion` doesn’t actually change the version of the stdlib that is depended on. Should it? I think this is a requirement for libraries that want to use 1.4 but not automatically drag the 1.4 stdilb into their consumers’ transitive deps, otherwise they need to explicitly configure dependency resolution – right?

Oh, you’re right, `-api-version` is not enough, you also need to tell the build to avoid adding dependency on the default kotlin-stdlib, and depend manually on 1.3 instead. And in this case, I suppose `-api-version` is not even useful anymore.

So instead of my initial advice, one should use Kotlin compiler 1.4, but with an explicit dependency on kotlin-stdlib 1.3. No need for `-api-version`. Then it will work as intended: 1.4 language features are enabled, 1.4 stdlib APIs are not.

(Note that telling the Kotlin compiler *1.3* to use language 1.4 is generally not OK for libraries because it moves the compiler into the “pre-release” mode so that produced binaries will not be readable by the released 1.4+ compilers.)

Is there a problem with depending on 1.4 stdlib if I don't use any 1.4 features?

I think I got this working, but you _also_ need `apiVersion` to avoid warnings. It’s a lot more work than just not upgrading to 1.4 at all.