Let you do a memberwise clone on a object of a base-type to an object of it's parent-type

Memberwise-Clone-Example.cs

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq;
using System.Reflection;

namespace ConsoleApplication1 {
    public class a {
        public string testa { get; set; }
        public virtual string Who() {
            return "I am class a!";
        }
    }

    public class b : a {
        public string testb { get; set; }
        public override string Who() {
            return "I am class b!";
        }
    }

    public static class Program {
        static void Main(string[] args) {
            var b = new b() { testa = "a", testb = "b" };

            //The version I use in my personal library is faster because it keeps a dictionary 
            //cache of the fields of each type, and creates get/set delegates 
            var a = b.CloneAs<a>();

            Debug.Assert(b.Who() == "I am class b!");
            Debug.Assert(((a)b).Who() == "I am class b!");
            Debug.Assert(a.Who() == "I am class a!");
            Debug.Assert(a.testa == "a");
        }

        public static T CloneAs<T>(this T input) where T : new() {
            var output = new T();
            output.CloneFrom(input);
            return output;
        }

        /// <summary>
        /// Updates one object with the fields of another.
        /// </summary>
        public static void CloneFrom<T>(this T ToObj, T FromObj) {
            CloneFrom(ToObj, FromObj, new Dictionary<object, object>());
        }

        private static FieldInfo[] GetMemberFields(this Type type) {
            return type.GetFields(BindingFlags.NonPublic | BindingFlags.Public | BindingFlags.Instance);
        }

        private static void CloneFrom<T>(T ToObj, T FromObj, Dictionary<object, object> Values) { 
            Values.Add(FromObj, ToObj); //The dictionary is used to prevent infinite recursion

            var fields = ToObj.GetType().GetMemberFields();
            object value = null;
            object othervalue = null;
            foreach (var field in fields) {
                value = field.GetValue(FromObj);
                othervalue = field.GetValue(ToObj);
                if (object.Equals(othervalue, value)) continue;

                if (value != null && Values.ContainsKey(value)) {
                    //Prevent recursive calls: objA.fieldB.fieldC = objA

                    field.SetValue(ToObj, Values[value]);
                } else if (othervalue != null && value != null && !field.FieldType.IsPrimitive && !field.FieldType.IsValueType && !(value is string)
                    && field.FieldType.GetMemberFields().Any()) {

                    //Do not overwrite object references
                    CloneFrom(othervalue, value, Values);
                } else {
                    field.SetValue(ToObj, value);
                }
            }
        }
    }
}