RouteValueDictionaryExtensions.cs

    public static class RouteValueDictionaryExtensions
    {
        public static RouteValueDictionary FlattenEnumerablesForLink(this RouteValueDictionary routeValueDictionary)
        {
            var result = new RouteValueDictionary();

            foreach (var key in routeValueDictionary.Keys)
            {
                var value = routeValueDictionary[key];

                var enumerableValue = value as IEnumerable;
                if (enumerableValue == null)
                {
                    if (value != null && value.GetType().IsClass)
                    {
                        throw new ApplicationException("Do not use class types as values in RouteValueDictionary. This does not generate useful links");
                    }

                    result[key] = value;
                    continue;
                }

                var elements = new List<object>(enumerableValue.Cast<object>());
                for (var index = 0; index < elements.Count; index++)
                {
                    var newKey = string.Format("{0}[{1}]", key, index);
                    result[newKey] = elements[index];
                }
            }

            return result;
        }
    }

RouteValueDictionaryExtensionsTests.cs

    class RouteValueDictionaryTests
    {
        [TestFixture]
        public class when_flattening_enumerables
        {
            [Test]
            public void then_should_flatten_enumerables_to_indexed_keys_array()
            {
                // Arrange
                var routeValueDictionary = new RouteValueDictionary();
                routeValueDictionary["Test"] = new[] {1, 2, 3};

                // Act
                var flatRouteValueDictionary = routeValueDictionary.FlattenEnumerablesForLink();

                // Assert
                Assert.That(flatRouteValueDictionary,
                    Has.Exactly(1)
                        .Matches<KeyValuePair<string, object>>(pair => pair.Key == "Test[0]" && (int)pair.Value == 1)
                        .And.Exactly(1)
                        .Matches<KeyValuePair<string, object>>(pair => pair.Key == "Test[1]" && (int)pair.Value == 2)
                        .And.Exactly(1)
                        .Matches<KeyValuePair<string, object>>(pair => pair.Key == "Test[2]" && (int)pair.Value == 3));
            }
        }
    }