Why doesn't the $watch in the directive work?

Question

Angular

Good day.
I am writing a directive, the essence of which is to call a modal window and send data to the server from a form in this window. I show the window using the Modal directive from Bootstrap components for Angular ( angular-ui.github.io/bootstrap ).
'templates/modal/addCom.html'

<select class="form-control" ng-model="selected">
    <option ng-repeat="type in types" value="{{type}}">{{type.comment}}</option>
</select>

app.directive('addCom',function($modal,addComService){
    return {
        restrict: 'A',
        link : function($scope, $element, $attributes){
            $element.on('click',function(){
                modal();
            });

            var modal = function(){
                var modalInstance = $modal.open({
                    animation: $scope.animationsEnabled,
                    templateUrl: 'templates/modal/addCom.html',
                    controller: function($scope,$modalInstance){

                        $scope.selected = {};
                        $scope.disabled = true;

                        $scope.$watch(
                            function(){
                                return $scope.selected;
                            },
                            function(newVal,oldVal){
                                //срабатывает только при вызове окна 
                                console.log(newVal);
                                //срабатывает только при вызове окна 
                                console.log(oldVal);
                            },
                            true
                        );

                    }
                })
            };
        }
    }
});

$watch only fires when the modal is opened. When the model changes, the selected $watch does not work, although if you display the value of the model in the view, you can see that the data is changing.

Answer 1

scalars in scopes are not inherited, as they are passed by value. Variants, store data in an object, they are passed by reference and references are inherited.