NgModel with ngSwitch, can't watch string variables?

I'm having trouble using $scope.$watch

for some angular variables that I have in my project scope. I made a sample jsfiddle to illustrate the problem.

Basically, I can use $scope.$watch

any model as ng-switch

long as it is an object. If it is a string, it will not invoke the clock expression and will not be modified outside the scope ng-switch

. angular copies the original string instead of passing it by reference, like an object?

I am using ng-repeat

for some elements - here are some of my code:

<div ng-switch="key">

          <div ng-switch-when="deal_id">
              DEALID: <input type="text" ng-model="dealIdModel"/> -- {{dealIdModel}}
          </div>
          <div ng-switch-when="thing_id">
              THING: <input type="text" ng-model="thingIdModel.test"/> -- {{thingIdModel.test}}
          </div>
          <div ng-switch-default>
              DEFAULT: <input type="text" placeholder="email" ng-model="items.params.email"/> -- {{items.params.email}}
          </div>

        </div>

      

        
        
        
      

    

And JS:

$scope.items = {
        "statusCode":"ACTIVE",
        "params":{
          "deal_id":"",
          "thing_id":"",
            "email":"Change me! I will get called"
        }
    };

    $scope.dealIdModel = "I won't change outside of the loop or get called.";
    $scope.thingIdModel = {test:'Change me! So will I!'};

    $scope.$watch('items.params.email', function (now, then, scope) {
        console.log('email change', now, then);
    });

    $scope.$watch('thingIdModel.test', function(now, then, scope) {
       console.log('changed the thing', now, then);   
    });

    $scope.$watch('dealIdModel', function(now, then, scope) {
        console.log('dealID changed:', now, then); 
    });