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Viewing / Editing File: array-set.js

/* -*- 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
 */

/**
 * 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.
 */
class ArraySet {
  constructor() {
    this._array = [];
    this._set = new Map();
  }

/**
   * Static method for creating ArraySet instances from an existing array.
   */
  static fromArray(aArray, aAllowDuplicates) {
    const set = new ArraySet();
    for (let 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
   */
  size() {
    return this._set.size;
  }

/**
   * Add the given string to this set.
   *
   * @param String aStr
   */
  add(aStr, aAllowDuplicates) {
    const isDuplicate = this.has(aStr);
    const idx = this._array.length;
    if (!isDuplicate || aAllowDuplicates) {
      this._array.push(aStr);
    }
    if (!isDuplicate) {
      this._set.set(aStr, idx);
    }
  }

/**
   * Is the given string a member of this set?
   *
   * @param String aStr
   */
  has(aStr) {
      return this._set.has(aStr);
  }

/**
   * What is the index of the given string in the array?
   *
   * @param String aStr
   */
  indexOf(aStr) {
    const idx = this._set.get(aStr);
    if (idx >= 0) {
        return idx;
    }
    throw new Error('"' + aStr + '" is not in the set.');
  }

/**
   * What is the element at the given index?
   *
   * @param Number aIdx
   */
  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.
   */
  toArray() {
    return this._array.slice();
  }
}
exports.ArraySet = ArraySet;

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