toMutableMap
Returns a new mutable map containing all key-value pairs from the original map.
fun <K, V> Map<out K, V>.toMutableMap(): MutableMap<K, V>(source)
fun main() {
val immutable = mapOf("a" to 1, "b" to 2)
val mutable = immutable.toMutableMap()
mutable["c"] = 3
mutable.remove("a")
println(mutable) // prints {b=2, c=3}
}