31 Computed properties

A computed property presents accessor behavior with field-like syntax.

class Counter {
  Integer stored

  Counter(Integer initial) {
    stored = initial
  }

  Integer value {
    get { return stored }
    set(next) { stored = next }
  }
}

main() {
  Counter counter = Counter(initial: 2)
  counter.value = 5
  printLine(counter.value)
}

Expected output:

5

stored is the backing field. Reading value invokes get, while assigning it invokes set(next); the property itself occupies no separate stored field. Remove the setter to make this property read-only.

Try it: Make the setter add one and observe the later read.

Precise rules: Reference.