array-set.js #1

/* -*- Mode: js; js-indent-level: 2; -*- */
/*
 * Copyright 2011 Mozilla Foundation and contributors
 * Licensed under the New BSD license. See LICENSE or:
 * http://opensource.org/licenses/BSD-3-Clause
 */
{
  var util = require('./util');

  /**
   * A data structure which is a combination of an array and a set. Adding a new
   * member is O(1), testing for membership is O(1), and finding the index of an
   * element is O(1). Removing elements from the set is not supported. Only
   * strings are supported for membership.
   */
  function ArraySet() {
    this._array = [];
    this._set = {};
  }

  /**
   * Static method for creating ArraySet instances from an existing array.
   */
  ArraySet.fromArray = function ArraySet_fromArray(aArray, aAllowDuplicates) {
    var set = new ArraySet();
    for (var i = 0, len = aArray.length; i < len; i++) {
      set.add(aArray[i], aAllowDuplicates);
    }
    return set;
  };

  /**
   * Return how many unique items are in this ArraySet. If duplicates have been
   * added, than those do not count towards the size.
   *
   * @returns Number
   */
  ArraySet.prototype.size = function ArraySet_size() {
    return Object.getOwnPropertyNames(this._set).length;
  };

  /**
   * Add the given string to this set.
   *
   * @param String aStr
   */
  ArraySet.prototype.add = function ArraySet_add(aStr, aAllowDuplicates) {
    var sStr = util.toSetString(aStr);
    var isDuplicate = this._set.hasOwnProperty(sStr);
    var idx = this._array.length;
    if (!isDuplicate || aAllowDuplicates) {
      this._array.push(aStr);
    }
    if (!isDuplicate) {
      this._set[sStr] = idx;
    }
  };

  /**
   * Is the given string a member of this set?
   *
   * @param String aStr
   */
  ArraySet.prototype.has = function ArraySet_has(aStr) {
    var sStr = util.toSetString(aStr);
    return this._set.hasOwnProperty(sStr);
  };

  /**
   * What is the index of the given string in the array?
   *
   * @param String aStr
   */
  ArraySet.prototype.indexOf = function ArraySet_indexOf(aStr) {
    var sStr = util.toSetString(aStr);
    if (this._set.hasOwnProperty(sStr)) {
      return this._set[sStr];
    }
    throw new Error('"' + aStr + '" is not in the set.');
  };

  /**
   * What is the element at the given index?
   *
   * @param Number aIdx
   */
  ArraySet.prototype.at = function ArraySet_at(aIdx) {
    if (aIdx >= 0 && aIdx < this._array.length) {
      return this._array[aIdx];
    }
    throw new Error('No element indexed by ' + aIdx);
  };

  /**
   * Returns the array representation of this set (which has the proper indices
   * indicated by indexOf). Note that this is a copy of the internal array used
   * for storing the members so that no one can mess with internal state.
   */
  ArraySet.prototype.toArray = function ArraySet_toArray() {
    return this._array.slice();
  };

  exports.ArraySet = ArraySet;
}