isolated scopes.

&.js

//
angular.module("MyApp", [])  
  .controller("MathCtrl", function($scope) {
    $scope.add = function(x, y) {
      return x + y;
    };
  })
  .directive("myAddThings", function() {
    return {
      restrict: "E",
      template: "{{result}}",
      scope: {
        localFn: "&fn"
      },
      link: function(scope) {
        scope.result = scope.localFn({
          x: 1,
          y: 2
        });
      }
    };
  });
  
  scope.result = scope.localFn({  
  x: 1,
  y: 2
});
//See how here in the HTML you have...

<my-add-things fn="add(x, y)"></my-add-things>  

=.js

//http://jonathancreamer.com/working-with-all-the-different-kinds-of-scopes-in-angular/

//=
angular.module("MyApp", [])  
  .controller("UserCtrl", function($scope) {
    $scope.loggedInUser = {
      name: "Austin Powers"
    }
  })
  .directive("myUserDirective", function() {
    return {
      restrict: "E",
      template: "<input ng-model='user.name' /></div>",
      scope: {
        user: "="
      },
      link: function(scope) {
        console.log(scope.user) // { name: "Austin Powers" }
      }
    };
  });
//You would then use this directive like...

<my-user-directive user="loggedInUser"></my-user-directive>  

@.js

angular.module("MyApp", [])  
  .controller("UserCtrl", function($scope) {
    $scope.loggedInUser = {
      firstName: "Austin",
      middleName: "Danger",
      lastName: "Powers"
    };
  })
  .directive("myUserDirective", function() {
    return {
      restrict: "E",
      template: "{{fullName}}",
      scope: {
        fullName: "@name"
      }
    };
  });
//And this is how you would use that directive...

<my-user-directive  
        name="{{loggedInUser.firstName}} {{loggedInUser.middleName}} {{loggedInUser.lastName}}">
        </my-user-directive>