    /**
     * @class Ext.util.MixedCollection
     * <p>
     * Represents a collection of a set of key and value pairs. Each key in the MixedCollection
     * must be unique, the same key cannot exist twice. This collection is ordered, items in the
     * collection can be accessed by index  or via the key. Newly added items are added to
     * the end of the collection. This class is similar to {@link Ext.util.HashMap} however it
     * is heavier and provides more functionality. Sample usage:
     * <pre><code>
    var coll = new Ext.util.MixedCollection();
    coll.add('key1', 'val1');
    coll.add('key2', 'val2');
    coll.add('key3', 'val3');

    console.log(coll.get('key1')); // prints 'val1'
    console.log(coll.indexOfKey('key3')); // prints 2
     * </code></pre>
     *
     * <p>
     * The MixedCollection also has support for sorting and filtering of the values in the collection.
     * <pre><code>
    var coll = new Ext.util.MixedCollection();
    coll.add('key1', 100);
    coll.add('key2', -100);
    coll.add('key3', 17);
    coll.add('key4', 0);
    var biggerThanZero = coll.filterBy(function(value){
        return value > 0;
    });
    console.log(biggerThanZero.getCount()); // prints 2
     * </code></pre>
     * </p>
     *
     * @constructor
     * @param {Boolean} allowFunctions Specify <tt>true</tt> if the {@link #addAll}
     * function should add function references to the collection. Defaults to
     * <tt>false</tt>.
     * @param {Function} keyFn A function that can accept an item of the type(s) stored in this MixedCollection
     * and return the key value for that item.  This is used when available to look up the key on items that
     * were passed without an explicit key parameter to a MixedCollection method.  Passing this parameter is
     * equivalent to providing an implementation for the {@link #getKey} method.
     */
    Ext.define('Ext.util.MixedCollection', {
        extend: 'Ext.util.AbstractMixedCollection',
        mixins: {
            sortable: 'Ext.util.Sortable'
        },

        constructor: function() {
            var me = this;
            me.callParent(arguments);
            me.addEvents('sort');
            me.mixins.sortable.initSortable.call(me);
        },

        doSort: function(sorterFn) {
            this.sortBy(sorterFn);
        },

        /**
         * @private
         * Performs the actual sorting based on a direction and a sorting function. Internally,
         * this creates a temporary array of all items in the MixedCollection, sorts it and then writes
         * the sorted array data back into this.items and this.keys
         * @param {String} property Property to sort by ('key', 'value', or 'index')
         * @param {String} dir (optional) Direction to sort 'ASC' or 'DESC'. Defaults to 'ASC'.
         * @param {Function} fn (optional) Comparison function that defines the sort order.
         * Defaults to sorting by numeric value.
         */
        _sort : function(property, dir, fn){
            var me = this,
                i, len,
                dsc   = String(dir).toUpperCase() == 'DESC' ? -1 : 1,

                //this is a temporary array used to apply the sorting function
                c     = [],
                keys  = me.keys,
                items = me.items;

            //default to a simple sorter function if one is not provided
            fn = fn || function(a, b) {
                return a - b;
            };

            //copy all the items into a temporary array, which we will sort
            for(i = 0, len = items.length; i < len; i++){
                c[c.length] = {
                    key  : keys[i],
                    value: items[i],
                    index: i
                };
            }

            //sort the temporary array
            Ext.Array.sort(c, function(a, b){
                var v = fn(a[property], b[property]) * dsc;
                if(v === 0){
                    v = (a.index < b.index ? -1 : 1);
                }
                return v;
            });

            //copy the temporary array back into the main this.items and this.keys objects
            for(i = 0, len = c.length; i < len; i++){
                items[i] = c[i].value;
                keys[i]  = c[i].key;
            }

            me.fireEvent('sort', me);
        },

        /**
         * Sorts the collection by a single sorter function
         * @param {Function} sorterFn The function to sort by
         */
        sortBy: function(sorterFn) {
            var me     = this,
                items  = me.items,
                keys   = me.keys,
                length = items.length,
                temp   = [],
                i;

            //first we create a copy of the items array so that we can sort it
            for (i = 0; i < length; i++) {
                temp[i] = {
                    key  : keys[i],
                    value: items[i],
                    index: i
                };
            }

            Ext.Array.sort(temp, function(a, b) {
                var v = sorterFn(a.value, b.value);
                if (v === 0) {
                    v = (a.index < b.index ? -1 : 1);
                }

                return v;
            });

            //copy the temporary array back into the main this.items and this.keys objects
            for (i = 0; i < length; i++) {
                items[i] = temp[i].value;
                keys[i]  = temp[i].key;
            }

            me.fireEvent('sort', me, items, keys);
        },

        /**
         * Reorders each of the items based on a mapping from old index to new index. Internally this
         * just translates into a sort. The 'sort' event is fired whenever reordering has occured.
         * @param {Object} mapping Mapping from old item index to new item index
         */
        reorder: function(mapping) {
            var me = this,
                items = me.items,
                index = 0,
                length = items.length,
                order = [],
                remaining = [],
                oldIndex;

            me.suspendEvents();

            //object of {oldPosition: newPosition} reversed to {newPosition: oldPosition}
            for (oldIndex in mapping) {
                order[mapping[oldIndex]] = items[oldIndex];
            }

            for (index = 0; index < length; index++) {
                if (mapping[index] == undefined) {
                    remaining.push(items[index]);
                }
            }

            for (index = 0; index < length; index++) {
                if (order[index] == undefined) {
                    order[index] = remaining.shift();
                }
            }

            me.clear();
            me.addAll(order);

            me.resumeEvents();
            me.fireEvent('sort', me);
        },

        /**
         * Sorts this collection by <b>key</b>s.
         * @param {String} direction (optional) 'ASC' or 'DESC'. Defaults to 'ASC'.
         * @param {Function} fn (optional) Comparison function that defines the sort order.
         * Defaults to sorting by case insensitive string.
         */
        sortByKey : function(dir, fn){
            this._sort('key', dir, fn || function(a, b){
                var v1 = String(a).toUpperCase(), v2 = String(b).toUpperCase();
                return v1 > v2 ? 1 : (v1 < v2 ? -1 : 0);
            });
        }
    });