read-only collections.kt

// mapOf is the read-only version of mutableMapof
val colors =  mapOf(
  "red" to 0xff0000,
  "green" to 0x00ff00,
  "blue" to 0x0000ff
)
val updatedColors = colors.plus("teal" to 0x008080) // doesn't change the original - it returns a new map


// listOf is the read-only version of mutableListof
val houses = listOf("Stark", "Lannister", "Tyrell", "Arryn", "Targaryen", "Martell", "Baratheon")
// Methods that return a new list instead of modifying it are still available:
var updatedHouses = houses.take(3).map {it.toUpperCase()} //["STARK", "LANNISTER", "TYRELL"]
// Adding new items requires copying the whole original one and making sure the new copy is also immutable
var updatedHouses = houses.toMutableList().apply{ add("Martell") }.toList()