Extending AngularJs Directives

gistfile1.js

'use strict';

angular.module('extndApp')
    .directive('parent', function () {
        return {
            template: '<div>' +
            '<ul>' +
            '<li>Hello</li>' +
            '<li>World</li>' +
            '<li>Foo</li>' +
            '<li>Bar</li>' +
            '</ul>' +
            '</div>',
            restrict: 'E',
            link: function postLink() {

                console.log('this is the parent function');
            }
        };
    });

angular.module('extndApp')
    .directive('child', function (parentDirective) {

        var child = angular.extend({}, parentDirective[0]);


        child.template = '<div>This is the child element</div>';

        return child;
    });

The only thing is you cannot seem to overwrite the link function. And the syntax for accessing the directive object literal is funky parentDirective[0]