using System;

using System.Diagnostics;

using System.Reflection;

using System.Collections.Generic;

using System.Linq;

using System.Linq.Expressions;

public class Program

{

    public static void Main()

    {

        var poco = new POCO();

        poco.Prop1 = "a";

        poco.Prop2 = "B";

​

​

        poco.SaveState();

​

        poco.Prop2 = "b";

​

        Console.WriteLine(poco.HasChangedSlow("Prop1"));

        Console.WriteLine(poco.HasChangedSlow("Prop2"));

        var watch = new Stopwatch();

        watch.Start();

        ThousandSlowTests(poco);

        watch.Stop();

        Console.WriteLine(watch.ElapsedTicks);

        watch.Reset();

        watch.Start();

        ThousandFastTests(poco);

        watch.Stop();

        Console.WriteLine(watch.ElapsedTicks);

    }

    public static void ThousandSlowTests(POCO poco) 

    {

        poco.Prop1 = 0.ToString();

        poco.SaveState();

        for (var i = 0; i<1000; i++) 

        {

            poco.Prop1 = i.ToString();

            poco.HasChangedSlow("Prop1");

        }

    }

    public static void ThousandFastTests(POCO poco) 

    {

        poco.Prop1 = 0.ToString();

        poco.SaveState();

        for (var i = 0; i<1000; i++) 

        {

​

            poco.Prop1 = i.ToString();

            poco.HasChangedFast("Prop1");

        }

    }

}

​

public class POCO : HasChangedBase

{

    public string Prop1 {get;set;}

    public string Prop2 {get;set;}

}

​

public class HasChangedBase 

{

    private class PropertyState

    {

        public PropertyInfo Property { get; set; }

        public object Value { get; set; }

        public Func<object, object> Getter { get; set; }

    }

​

    private Dictionary<string, PropertyState> propertyStore;

    public void SaveState() 

    {

        propertyStore = this

            .GetType()

            .GetProperties()

            .ToDictionary(

                p => p.Name, 

                p => 

                {

                    var getter = HasChangedBase.BuildUntypedGetter(p);

                    return new PropertyState

                    { 

                        Property = p, 

                        Value = getter(this),

                        Getter = getter,

                    };

                });

    }

    public bool HasChangedFast(string propertyName) 

    {

        return propertyStore != null 

            && propertyStore.ContainsKey(propertyName) 

            && propertyStore[propertyName].Value != propertyStore[propertyName].Getter(this);

    }

​

    public bool HasChangedSlow(string propertyName) 

    {

        return propertyStore != null 

            && propertyStore.ContainsKey(propertyName) 

            && propertyStore[propertyName].Value != propertyStore[propertyName].Property.GetValue(this);

    }

    public static Func<object, object> BuildUntypedGetter(PropertyInfo propertyInfo)

    {

        var targetType = propertyInfo.DeclaringType;

        var methodInfo = propertyInfo.GetGetMethod();

        var returnType = methodInfo.ReturnType;

​

        var exTarget = Expression.Parameter(typeof(object), "t");

        var exBody = Expression.Call(Expression.Convert(exTarget, targetType), methodInfo);

        var exBody2 = Expression.Convert(exBody, typeof(object));

​

        var lambda = Expression.Lambda<Func<object, object>>(exBody2, exTarget);

​

        var action = lambda.Compile();

        return action;

    }

}