How to find the KClass of the owner of a companion object? - kotlin

Question

I'm trying to get the class that owns a companion object so I can create loggers with inline technique inside a companion object but referencing the main class that is being logged and not the companion object.
The problem is that I can't find a way to get the owner of the companion object, how can I do it?
fun Logger(c: Class<*>): Logger {
var c2 = c
val k = c.kotlin
if (k.isCompanion) {
c2 = k.<opposite of what companionObject does>.java
}
// Calls a factory, reuse the same instance if it already exists
return RootLogger.getChild(c2)
}
#Suppress("NOTHING_TO_INLINE")
inline fun Logger(): Logger {
return Logger(MethodHandles.lookup().lookupClass())
}
The intended use-cases:
A:
class SomeClass {
companion object {
// Logger is inside a companion object
// But it must be the same as if it were created directly inside `SomeClass`
private val log = Logger()
}
fun someFun() = log.info("Hello")
}
B:
// can be object or anything else
class SomeClass {
// The same object is returned to all instances and would be the same object
// as if it were inside a companion object
private val log = Logger()
fun someFun() = log.info("Hello")
}

Answer 1

In JVM environment that can be achieved with:
k.java.enclosingClass.kotlin
So the function would be:
fun Logger(c: Class<*>): Logger {
var c2 = c
val k = c.kotlin
if (k.isCompanion) {
c2 = k.java.enclosingClass
}
// Calls a factory, reuse the same instance if it already exists
return RootLogger.getChild(c2)
}
That can be tested with:
internal class LoggerTest {
#Test
internal fun testUseCaseA() {
val fqn = UseCaseA::class.qualifiedName
assertEquals(fqn, UseCaseA.log.name)
val log = Logger(UseCaseA::class.java)
assertEquals(fqn, log.name)
assertSame(UseCaseA.log, log)
val log2 = Logger(UseCaseA.Companion::class.java)
assertEquals(fqn, log2.name)
assertSame(log, log2)
}
#Test
internal fun testUseCaseB() {
val fqn = UseCaseB::class.qualifiedName
val b1 = UseCaseB()
assertEquals(fqn, b1.log.name)
val log = Logger(UseCaseB::class.java)
assertEquals(fqn, log.name)
assertSame(b1.log, log)
val b2 = UseCaseB()
assertEquals(fqn, b2.log.name)
assertSame(b2.log, log)
}
private class UseCaseA {
companion object {
val log = Logger()
}
}
private class UseCaseB {
val log = Logger()
}
}