val second = secondList.toSet()
val result = firstList.filter { it.someProperty in second }

fun main() {
  val contacts = listOf(Contact(1), Contact(2), Contact(4))
    val profiles = listOf(PublicProfile(1), PublicProfile(3), PublicProfile(4))
    println(contacts)
    populateContacts(contacts, profiles, { it.id }, { it.id })
    println(contacts)
}

data class Contact(val id: Long, var publicProfile: PublicProfile? = null)
data class PublicProfile(val id: Long)

fun <T> populateContacts(contacts: List<Contact>, profiles: List<PublicProfile>, contactSelector: (Contact) -> T, profileSelector: (PublicProfile) -> T) {
    val idToContacts = contacts.associateBy(contactSelector)
    val idToProfiles = profiles.associateBy(profileSelector)
    idToProfiles.forEach { (id, profile) -> idToContacts[id]?.let { it.publicProfile = profile }}
}