function ngDirective(directive) {
  if (isFunction(directive)) {
    directive = {
      link: directive
    };
  }
  directive.restrict = directive.restrict || 'AC';
  return valueFn(directive);
}
@ngdoc filter
@name orderBy
@function

@description
Orders a specified `array` by the `expression` predicate.

@param {Array} array The array to sort.
@param {function(*)|string|Array.<(function(*)|string)>} expression A predicate to be
   used by the comparator to determine the order of elements.

   Can be one of:

   - `function`: Getter function. The result of this function will be sorted using the
     `<`, `=`, `>` operator.
   - `string`: An Angular expression which evaluates to an object to order by, such as 'name'
     to sort by a property called 'name'. Optionally prefixed with `+` or `-` to control
     ascending or descending sort order (for example, +name or -name).
   - `Array`: An array of function or string predicates. The first predicate in the array
     is used for sorting, but when two items are equivalent, the next predicate is used.

@param {boolean=} reverse Reverse the order of the array.
@returns {Array} Sorted copy of the source array.

@example
   <example>
     <file name="index.html">
       <script>
         function Ctrl($scope) {
           $scope.friends =
               [{name:'John', phone:'555-1212', age:10},
                {name:'Mary', phone:'555-9876', age:19},
                {name:'Mike', phone:'555-4321', age:21},
                {name:'Adam', phone:'555-5678', age:35},
                {name:'Julie', phone:'555-8765', age:29}]
           $scope.predicate = '-age';
         }
       </script>
       <div ng-controller="Ctrl">
         <pre>Sorting predicate = {{predicate}}; reverse = {{reverse}}</pre>
         <hr/>
         [ <a href="" ng-click="predicate=''">unsorted</a> ]
         <table class="friend">
           <tr>
             <th><a href="" ng-click="predicate = 'name'; reverse=false">Name</a>
                 (<a href="" ng-click="predicate = '-name'; reverse=false">^</a>)</th>
             <th><a href="" ng-click="predicate = 'phone'; reverse=!reverse">Phone Number</a></th>
             <th><a href="" ng-click="predicate = 'age'; reverse=!reverse">Age</a></th>
           </tr>
           <tr ng-repeat="friend in friends | orderBy:predicate:reverse">
             <td>{{friend.name}}</td>
             <td>{{friend.phone}}</td>
             <td>{{friend.age}}</td>
           </tr>
         </table>
       </div>
     </file>
   </example>