mutable.kt

val mutable = MyValue.Mutable("Foo")
val immutable = MyValue.Immutable("Foo")

mutable.value = "Bar"    // This is fine

immutable.value = "Bar"  // This will not compile because value cannot be reassigned

val mutated = immutable.mutate()
mutated.value = "Bar"    // This is fine

immutable.value = "Bar"  // This will not compile because value cannot be reassigned

val immutated = mutated.immutate()

immutated.value = "Bar"  // This will not compile because value cannot be reassigned