A property is a value of an object which is used like a field, but which actually results in a function call when getting its value and a method call when setting its value. There are many advantages of properties, such as:

  1. The ability to perform additional actions when a property is set
  2. The ability to compute property values at runtime, without having to store them in the object
  3. The ability to override property behaviors by subclassing

Properties are defined using a syntax very similar to fields:

property size:Int

Unlike a field, this declaration does not increase the size of a the object containing it or otherwise allocate memory to store the size property. Instead, whenever the size property is read, a function named get_size() is called, and whenever the size property is written, a method named set_size() is called. Here is a complete, working property example:

class Zeroes {
    def contents:Array<Int>

    property size:Int

    function get_size():Int {
        return contents.count

    method set_size(size:Int) {
        while contents.count > size {
        while contents.count < size {< size {

    function convert():String {
        return contents.convert()

method main() {
    def z := Zeroes()
    Console.printLine(z.size) -- prints "0"
    z.size := 5
    Console.printLine(z) -- prints [0, 0, 0, 0, 0]

It is possible to create a read-only or write-only property by defining only the set_ or get_ method, respectively, but at least one of the two must be defined.