using System;

using System.Collections.Generic;

using System.Linq.Expressions;

using System.Linq;

using System.Diagnostics;

public class Program

{ public class A

        {

            public int Id { get; set; }

            public string Name { get; set; }

        }

​

        public static Func<TEntity, bool> GetComparer<TEntity, TProperty>(Expression<Func<TEntity, TProperty>> selector, TProperty value)

        {

            var propertyRef = selector.Body;

            var parameter = selector.Parameters[0];

            var constantRef = Expression.Constant(value);

            var comparer    = Expression.Lambda<Func<TEntity, bool>>

                    (Expression.Equal(propertyRef, constantRef), parameter)

                    .Compile();

            return comparer;

        }

       public static ICollection<A> CreateData()

        {

            var list = new List<A>();

            var id = 1;

            var rand = new Random();

            for (int i = 0; i < 100000; i++)

            {

                list.Add(new A

                {

                    Id = id++,

                    Name = rand.Next(2) == 1 ? "A" : "B"

                });

            }

​

            return list;

        }

    public static void Main()

    {

               var list = CreateData();

            var sw = new Stopwatch();

            var compsw = new Stopwatch();

            int[] counts = new int[3];

            sw.Start();

            foreach (var a in list.Where(x => x.Name == "A"))

            {

                counts[0]++;

            }

            sw.Stop();

            Console.WriteLine("Using LINQ with known parameter (Base line): {0}ms", sw.ElapsedMilliseconds);

​

            sw.Reset();

​

            sw.Start();

            compsw.Start();

            var comp = GetComparer((A x) => x.Name, "A");

            compsw.Stop();

            foreach (var a in list.Where(comp))

            {

                counts[1]++;

            }

            sw.Stop();

​

            Console.WriteLine("Using compiled expression: {0}ms, compilation time: {1}ms", sw.ElapsedMilliseconds, compsw.ElapsedMilliseconds);

​

            sw.Reset();

​

            sw.Start();

​

            foreach (var a in list.Where(x => x.GetType().GetProperty("Name").GetValue(x).ToString() == "A"))

            {

                counts[2]++;

            }

            sw.Stop();

​

            Console.WriteLine("Using reflection: {0}ms", sw.ElapsedMilliseconds);

​

            if (counts[0] != counts[1] || counts[0] != counts[2] || counts[1] != counts[2])

            {

                Console.WriteLine("there was an error in test {0} {1} {2}", counts[0], counts[1], counts[2]);

            }

            else

            {

                Console.WriteLine("{0} {1} {2}", counts[0], counts[1], counts[2]);

            }

    }

}