Does kotlin have any way to generate random unique...

# announcements

[Andrey Stepankov]

Does kotlin have any way to generate random unique id in compile time. I mean id is random, but is const for runtime?

So i can write compiler plugin, but may be community already has solution.

For example:

// sourse
fun a(): String = CompileTimeId.nextId()

// compiled code
fun a(): String = "hdhdjdnwld"

[crummy]

hmm. Maybe you could hash your jar (if you're building for JVM)?

[Andrey Stepankov]

I can't i need more than one id with that logic.

[Steve]

Does it have to be constant between runs?

[crummy]

You could use Random() and seed it with a hash of the jar.

[Andrey Stepankov]

It must be constant in one run. Can be different between runs.

[crummy]

actually I'd seed it with the git sha of your latest commit, inject that with an environment variable (assuming you're building with git on a CI system)

[Steve]

then just generate a UUID at startup

[Andrey Stepankov]

I think i cant use random. Because if i call multiple times function a (see example below) result will be different.

[Steve]

just call it once and cache the result

[Andrey Stepankov]

Its so problematic to cache result. Exaclty by that reason i need const in compile time.

[Steve]

it's really not

[Steve]

at startup, generate your UUID, and then just use that

[Andrey Stepankov]

Ok. Some more real example of usage.
I cant modify constructor and i really dont like to use singleton in this case.
class A {
val id = CompileTimeId()
}

[crummy]

val id = IdGenerator().getFirstId()

[crummy]

class IdGenerator {
val rng = Random(System.env("GIT_SHA"))
val firstId = rng.next()
val secondId = rng.next()
}

[crummy]

don't actually know how seeding works but maybe you get the idea?

[Andrey Stepankov]

Ок. Add another class B with simular logic.

B().id == A().id?

[Andrey Stepankov]

I think ids will be same. Its not unique.

[crummy]

if they use the same seed, and id is called in the same order, yes

[crummy]

class B { val rng = Random(System.env("GIT_SHA") + "classb") }
class A { val rng = Random(System.env("GIT_SHA") + "classa") }

[crummy]

now they'll be different

[Andrey Stepankov]

Yes. But now we have unique strings. classa and classb. In that case i can write ids by hands.

[crummy]

the id would still be generated by rng.next()

[Andrey Stepankov]

Yes. Its no difference between 'classa' and 'result_from_random' because its unique.

[crummy]

how about https://pl.kotl.in/qcqz1WnRg

[Andrey Stepankov]

Thank you. Its can be works.