gecko-dev/xpcom/ds/nsIArrayExtensions.idl

/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#include "nsIArray.idl"

/**
 * Helper interface for allowing scripts to treat nsIArray instances as if
 * they were nsISupportsArray instances while iterating.
 *
 * nsISupportsArray is convenient to iterate over in JavaScript:
 *
 * for (let i = 0; i < array.Count(); ++i) {
 *   let elem = array.GetElementAt(i);
 *   ...
 * }
 *
 * but doing the same with nsIArray is somewhat less convenient, since
 * queryElementAt is not nearly so nice to use from JavaScript.  So we provide
 * this extension interface so interfaces that currently return
 * nsISupportsArray can start returning nsIArrayExtensions and all JavaScript
 * should Just Work. Eventually we'll roll this interface into nsIArray
 * itself, possibly getting rid of the Count() method, as it duplicates
 * nsIArray functionality.
 */
[scriptable, uuid(261d442e-050c-453d-8aaa-b3f23bcc528b)]
interface nsIArrayExtensions : nsIArray
{
  /**
   * Count()
   *
   * Retrieves the length of the array. This is an alias for the
   * |nsIArray.length| attribute.
   */
  uint32_t Count();

  /**
   * GetElementAt()
   *
   * Retrieve a specific element of the array. null is a valid result for
   * this method.
   *
   * Note: If the index is out of bounds null will be returned.
   *       This differs from the behavior of nsIArray.queryElementAt() which
   *       will throw if an invalid index is specified.
   *
   * @param index position of element
   */
  nsISupports GetElementAt(in uint32_t index);
};