snowl/modules/Mixins.js

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 * Version: MPL 1.1/GPL 2.0/LGPL 2.1
 *
 * The contents of this file are subject to the Mozilla Public License Version
 * 1.1 (the "License"); you may not use this file except in compliance with
 * the License. You may obtain a copy of the License at
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 *
 * Software distributed under the License is distributed on an "AS IS" basis,
 * WITHOUT WARRANTY OF ANY KIND, either express or implied. See the License
 * for the specific language governing rights and limitations under the
 * License.
 *
 * The Original Code is Snowl.
 *
 * The Initial Developer of the Original Code is Mozilla.
 * Portions created by the Initial Developer are Copyright (C) 2009
 * the Initial Developer. All Rights Reserved.
 *
 * Contributor(s):
 *   Myk Melez <myk@mozilla.org>
 *
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 * either the GNU General Public License Version 2 or later (the "GPL"), or
 * the GNU Lesser General Public License Version 2.1 or later (the "LGPL"),
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let EXPORTED_SYMBOLS = ["Mixins"];

/**
 * Mix attributes (properties, methods, getters/setters) from the source object
 * into the target object.
 *
 * Note: doesn't mix in attributes that already exist in the target object
 * (i.e. doesn't override existing attributes).
 * ??? Should it?
 * 
 * FIXME: give the target object access in some way to the source's version
 * of attributes it overrides.
 *
 * @param   source  {Object}  the object that provides attributes
 * @param   target  {Object}  the object that receives attributes
 */
function mixin(source, target) {
  for (let attribute in source) {
    // Don't mix in attributes that already exist in the target.
    if (attribute in target)
      continue;

    let getter = source.__lookupGetter__(attribute);
    let setter = source.__lookupSetter__(attribute);

    // We can have a getter, a setter, or both.  If we have either, we only
    // define one or both of them.  Otherwise, we assign the property directly.
    if (getter || setter) {
      if (getter)
        target.__defineGetter__(attribute, getter);
      if (setter)
        target.__defineSetter__(attribute, setter);
    }
    else
       target[attribute] = source[attribute];
  }
};

/**
 * Meld attributes, like mixin but recursive to include object hierarchy,
 *  for example to handle a JSON object.
 *
 * @param   source  {Object}  the object that provides attributes
 * @param   target  {Object}  the object that receives attributes
 * @param   keep    {Boolean} if true, source attributes not in the target are
 *                            retained; if false, the target does not get them.
 * @param   replace {Boolean} if true, source attribute replaces the same
 *                            attribute in the target are; if false, the target
 *                            retains its attribute value.
 * @param   logger  {Object}  reference to logging function
 */
function meldin(source, target, keep, replace, logger) {
  for (let attribute in source) {
    // Recursive mixin of objects of objects
    if (typeof source[attribute] == "object" && typeof target[attribute] == "object") {
      meldin(source[attribute], target[attribute], keep, replace, logger);
    }
    else {
      // Don't mix in attributes that already exist in the target, unless replace
      // is false.
      if (attribute in target && !replace)
        continue;

      // Don't add attributes in target but not in source to source if keep is false.
      if (!(attribute in target) && !keep)
        continue;

      let getter = source.__lookupGetter__(attribute);
      let setter = source.__lookupSetter__(attribute);

      // We can have a getter, a setter, or both.  If we have either, we only
      // define one or both of them.  Otherwise, we assign the property directly.
      if (getter || setter) {
        if (getter)
          target.__defineGetter__(attribute, getter);
      if (setter)
        target.__defineSetter__(attribute, setter);
      }
      else
         target[attribute] = source[attribute];
    }
  }
};

// FIXME: support both source and target arguments accepting arrays of objects.
let Mixins = {
  mix: function(source) {
    return {
      source: source,
      into: function(target) {
        mixin(this.source, target);
      }
    };
  },
  meld: function(source, keep, replace, logger) {
    return {
      source: source,
      into: function(target) {
        meldin(this.source, target, keep, replace, logger);
      }
    };
  },
};