gistfile1.cs

public class ParamsExtraction
    {
        Group group;
        public ParamsExtraction(Group group)
        {
            this.group = group;
        }

        private bool TryGet<T>(int position, out T result)
        {
            if (!group.Success) return Failure(out result);
            if (position >= group.Captures.Count) return Failure(out result);

            var str = group.Captures[position].Value;
            if (IsNonStringNullValue<T>(str)) return Failure(out result);

            var type = typeof(T).GetValueTypeIfNullable();
            result = (T)Convert.ChangeType(str, type);
            return true;

        }

        private static bool Failure<T>(out T result)
        {
            result = default(T);
            return false;
        }

        private static bool IsNonStringNullValue<T>(string str)
        {
            return (typeof(T) != typeof(string) && str.Trim().IsNullOrEmpty());
        }

        public T Required<T>(int position)
        {
            T result;
            if (!TryGet(position, out result))
                throw new ArgumentOutOfRangeException("required positional parameter {0} not found".AsFormat(position));
            return result;
        }

        public T Optional<T>(int position)
        {
            T result;
            TryGet(position, out result);
            return result;
        }
    }