    /**
     * Represents a single sorter that can be used as part of the sorters configuration in Ext.mixin.Sortable.
     */
    Ext.define('Ext.util.Sorter', {
        isSorter: true,

        config: {
            /**
             * @cfg {String} property The property to sort by. Required unless `sorterFn` is provided
             */
            property: null,

            /**
             * @cfg {Function} sorterFn A specific sorter function to execute. Can be passed instead of {@link #property}
             */
            sorterFn: null,

            /**
             * @cfg {String} root Optional root property. This is mostly useful when sorting a Store, in which case we set the
             * root to 'data' to make the filter pull the {@link #property} out of the data object of each item
             */
            root: null,

            /**
             * @cfg {Function} transform A function that will be run on each value before
             * it is compared in the sorter. The function will receive a single argument,
             * the value.
             */
            transform: null,

            /**
             * @cfg {String} direction The direction to sort by.
             */
            direction: "ASC",

            /**
             * @cfg {Mixed} id An optional id this sorter can be keyed by in Collections. If
             * no id is specified it will use the property name used in this Sorter. If no
             * property is specified, e.g. when adding a custom sorter function we will generate
             * a random id.
             */
            id: undefined
        },

        constructor: function(config) {
            this.initConfig(config);
        },

        // <debug>
        applySorterFn: function(sorterFn) {
            if (!sorterFn && !this.getProperty()) {
                Ext.Logger.error("A Sorter requires either a property or a sorterFn.");
            }
            return sorterFn;
        },

        applyProperty: function(property) {
            if (!property && !this.getSorterFn()) {
                Ext.Logger.error("A Sorter requires either a property or a sorterFn.");
            }
            return property;
        },
        // </debug>

        applyId: function(id) {
            if (!id) {
                id = this.getProperty();
                if (!id) {
                    id = Ext.id(null, 'ext-sorter-');
                }
            }

            return id;
        },

        /**
         * @private
         * Creates and returns a function which sorts an array by the given property and direction
         * @return {Function} A function which sorts by the property/direction combination provided
         */
        createSortFunction: function(sorterFn) {
            var me        = this,
                modifier  = me.getDirection().toUpperCase() == "DESC" ? -1 : 1;

            //create a comparison function. Takes 2 objects, returns 1 if object 1 is greater,
            //-1 if object 2 is greater or 0 if they are equal
            return function(o1, o2) {
                return modifier * sorterFn.call(me, o1, o2);
            };
        },

        /**
         * @private
         * Basic default sorter function that just compares the defined property of each object
         */
        defaultSortFn: function(item1, item2) {
            var me = this,
                transform = me._transform,
                root = me._root,
                value1, value2,
                property = me._property;

            if (root !== null) {
                item1 = item1[root];
                item2 = item2[root];
            }

            value1 = item1[property];
            value2 = item2[property];

            if (transform) {
                value1 = transform(value1);
                value2 = transform(value2);
            }

            return value1 > value2 ? 1 : (value1 < value2 ? -1 : 0);
        },

        updateDirection: function() {
            this.updateSortFn();
        },

        updateSortFn: function() {
            this.sort = this.createSortFunction(this.getSorterFn() || this.defaultSortFn);
        },

        /**
         * Toggles the direction of this Sorter. Note that when you call this function,
         * the Collection this Sorter is part of does not get refreshed automatically.
         */
        toggle: function() {
            this.setDirection(Ext.String.toggle(this.getDirection(), "ASC", "DESC"));
        }
    });