55 Bound method references

counter.add becomes a function value bound to that particular counter. Invoking add(2) updates the same object's field.

class Counter {
  Integer value

  Integer add(Integer amount) {
    value = value + amount
    return value
  }
}

main() {
  Counter counter = Counter(value: 10)
  Integer add(Integer amount) = counter.add
  printLine(add(2))
  printLine(counter.value)
}

Expected output:

12
12

Try it: Create another counter and bind its add method separately.

Precise rules: Reference.