Bind array of boolean in angularjs directive

In my view, I have:

<input my-directive
       inputs="[userData.var1, userData.var2]"
       type="checkbox"
       ng-model="userData.myModel"
       id="vegetarian"
       class="v3-custom-checkbox" />

In the directive, I have:

myDirectives.directive('myDirective', function() {
    return {
    restrict: 'A',
    require: 'ngModel',
    scope: {
        inputs: '='
    },
    link: function(scope, element, attrs, ngModel) {
        scope.$watch(function () {
            return ngModel.$modelValue;
        }, function(newValue) {
            if(newValue) {
                 for (var i = 0; i < scope.inputs.length; i++) {
                     scope.inputs[i]=false;
                 }
                 console.log(scope.inputs);
            }
        });
    }
}

This gives me an error expression in attribute 'inputs' is non-assignable!

Angular version is 1.6.4.