--- /dev/null
+
+/**
+ * Module dependencies.
+ */
+
+var Symbol = require('es6-symbol');
+var debug = require('debug')('array-index');
+
+var get = Symbol('get');
+var set = Symbol('set');
+var length = Symbol('length');
+
+/**
+ * JavaScript Array "length" is bound to an unsigned 32-bit int.
+ * See: http://stackoverflow.com/a/6155063/376773
+ */
+
+var MAX_LENGTH = Math.pow(2, 32);
+
+/**
+ * Module exports.
+ */
+
+module.exports = ArrayIndex;
+ArrayIndex.get = get;
+ArrayIndex.set = set;
+
+/**
+ * Subclass this.
+ */
+
+function ArrayIndex (_length) {
+ Object.defineProperty(this, 'length', {
+ get: getLength,
+ set: setLength,
+ enumerable: false,
+ configurable: true
+ });
+
+ this[length] = 0;
+
+ if (arguments.length > 0) {
+ setLength.call(this, _length);
+ }
+}
+
+/**
+ * You overwrite the "get" Symbol in your subclass.
+ */
+
+ArrayIndex.prototype[ArrayIndex.get] = function () {
+ throw new Error('you must implement the `ArrayIndex.get` Symbol');
+};
+
+/**
+ * You overwrite the "set" Symbol in your subclass.
+ */
+
+ArrayIndex.prototype[ArrayIndex.set] = function () {
+ throw new Error('you must implement the `ArrayIndex.set` Symbol');
+};
+
+/**
+ * Converts this array class into a real JavaScript Array. Note that this
+ * is a "flattened" array and your defined getters and setters won't be invoked
+ * when you interact with the returned Array. This function will call the
+ * getter on every array index of the object.
+ *
+ * @return {Array} The flattened array
+ * @api public
+ */
+
+ArrayIndex.prototype.toArray = function toArray () {
+ var i = 0;
+ var l = this.length;
+ var array = new Array(l);
+ for (; i < l; i++) {
+ array[i] = this[i];
+ }
+ return array;
+};
+
+/**
+ * Basic support for `JSON.stringify()`.
+ */
+
+ArrayIndex.prototype.toJSON = function toJSON () {
+ return this.toArray();
+};
+
+/**
+ * toString() override. Use Array.prototype.toString().
+ */
+
+ArrayIndex.prototype.toString = function toString () {
+ var a = this.toArray();
+ return a.toString.apply(a, arguments);
+};
+
+/**
+ * inspect() override. For the REPL.
+ */
+
+ArrayIndex.prototype.inspect = function inspect () {
+ var a = this.toArray();
+ Object.keys(this).forEach(function (k) {
+ a[k] = this[k];
+ }, this);
+ return a;
+};
+
+/**
+ * Getter for the "length" property.
+ * Returns the value of the "length" Symbol.
+ */
+
+function getLength () {
+ debug('getting "length": %o', this[length]);
+ return this[length];
+};
+
+/**
+ * Setter for the "length" property.
+ * Calls "ensureLength()", then sets the "length" Symbol.
+ */
+
+function setLength (v) {
+ debug('setting "length": %o', v);
+ return this[length] = ensureLength(this, v);
+};
+
+/**
+ * Ensures that getters/setters from 0 up to "_newLength" have been defined
+ * on `Object.getPrototypeOf(this)`.
+ *
+ * @api private
+ */
+
+function ensureLength (self, _newLength) {
+ var newLength;
+ if (_newLength > MAX_LENGTH) {
+ newLength = MAX_LENGTH;
+ } else {
+ newLength = _newLength | 0;
+ }
+ var proto = Object.getPrototypeOf(self);
+ var cur = proto[length] | 0;
+ var num = newLength - cur;
+ if (num > 0) {
+ var desc = {};
+ debug('creating a descriptor object with %o entries', num);
+ for (var i = cur; i < newLength; i++) {
+ desc[i] = setup(i);
+ }
+ debug('calling `Object.defineProperties()` with %o entries', num);
+ Object.defineProperties(proto, desc);
+ proto[length] = newLength;
+ }
+ return newLength;
+}
+
+/**
+ * Returns a property descriptor for the given "index", with "get" and "set"
+ * functions created within the closure.
+ *
+ * @api private
+ */
+
+function setup (index) {
+ function get () {
+ return this[ArrayIndex.get](index);
+ }
+ function set (v) {
+ return this[ArrayIndex.set](index, v);
+ }
+ return {
+ enumerable: true,
+ configurable: true,
+ get: get,
+ set: set
+ };
+}