withDefault

Returns a wrapper of this read-only map, having the implicit default value provided with the specified function defaultValue.

fun <K, V> Map<K, V>.withDefault(defaultValue: (key: K) -> V): Map<K, V>(source)

val map = mapOf(1 to "one", 2 to "two")
val mapWithDefault = map.withDefault { key -> "missing key $key" }

println(mapWithDefault[1])   // prints: one
println(mapWithDefault[3])   // prints: missing key 3

Source