inline fun <K, V, R, M : MutableMap<in R, in V>> Map<out K, V>.mapKeysTo(
    destination: M,
    transform: (Entry<K, V>) -> R
): M

Populates the given destination map with entries having the keys obtained by applying the transform function to each entry in this Map and the values of this map.

In case if any two entries are mapped to the equal keys, the value of the latter one will overwrite the value associated with the former one.