Immutable mutual assignments (https://stackoverflow.com/questions/50799240/kotlin-mutual-assignments/50802264#50802264)

Person.kt

class Person() {
    private lateinit var _other: Person

    private constructor(_other: Person) : this() {
        this._other = _other
    }

    val other: Person
        get() {
            if (!::_other.isInitialized) {
                _other = Person(this)
            }
            return _other
        }
}