19 Maps

A map associates a typed key with a typed value.

main() {
  Map<String, Integer> scores = Map<>()
  scores.put(key: "Ada", value: 3)
  scores.put(key: "Lin", value: 5)
  printLine(scores["Ada"])
  printLine(scores.containsKey("Lin"))
  printLine(scores.size())
  scores.put(key: "Ada", value: 7)
  printLine(scores["Ada"])
  printLine(scores.size())
}

Expected output:

3
true
2
7
2

put writes a key-value pair. The index read retrieves Ada's value, and containsKey checks another key. Writing Ada again replaces its value without increasing the entry count.

Try it: Write a new value for Ada and observe whether the entry count grows.

Precise rules: Reference.