a.rb

app.controller('HomeController', function($scope) {
  $scope.selectedMail;

  $scope.setSelectedMail = function(mail) {
    $scope.selectedMail = mail;
  };

  $scope.isSelected = function(mail) {
    if($scope.selectedMail) {
      return $scope.selectedMail === mail;
    }
  };
});

// directive that builds the email listing
app.directive('emailListing', function() {
  return {
    restrict: 'EA', // E- element A- attribute C- class M- comment
    replace: false, // whether angular should replace the element or append
    scope: { // may be true/false or hash. if a hash we create an 'isolate' scope
      email: '=', // accept an object as parameter
      action: '&', // accept a function as a parameter
      shouldUseGravatar: '@' // accept a string as a parameter
    },
    templateUrl: '/templates/emailListing.html',
    controller: ['$scope', '$element', '$attrs', '$transclude',
      function($scope, $element, $attrs, $transclude) {
        $scope.handleClick = function() {
          $scope.action({selectedMail: $scope.email});
          console.log($scope.isSelected);
        };
      }
    ]
  }
});