Lazy vs. Eager Evaluation

        /// <summary>
        /// This has lazy evaluation, so you won't find out if the argument is the cause of an exception 
        /// until you start the enumeration. 
        /// </summary>
        /// <param name="word"></param>
        /// <returns></returns>
        public static IEnumerable<char> MakeUpperCaseAndReturnParts (string word)
        {
            if (String.IsNullOrWhiteSpace(word))
            {
                throw new ArgumentException("input is null");
            }

            var uppercase = word.ToUpper();

            foreach(var c in uppercase)
            {
                yield return c;
            }

        }

        /// <summary>
        /// Since the enumeration is encapsulated in another function, the evaluation of the paratmer is 
        /// immediate, allowing you to notice the exception when the method is called
        /// and not evaulated at some later time. 
        /// </summary>
        /// <param name="word"></param>
        /// <returns></returns>
        public static IEnumerable<char> MakeUpperCaseAndReturnPartsLocalFunction (string word)
        {
            if (String.IsNullOrWhiteSpace(word))
            {
                throw new ArgumentException("input is null");
            }

            IEnumerable<char> EnumerateChars ()
            {
                var uppercase = word.ToUpper();

                foreach (var c in uppercase)
                {
                    yield return c;
                }
            }

            return EnumerateChars();
        }