using System;

using System.Linq.Expressions;

​

public class SecretKeeper

{

    private int _secret;

    public int Secret{get { return _secret; } set { _secret = value; }}

}

​

public static class Ext

{

    public static int GetSecretUsingExpressionTrees(this SecretKeeper keeper)

    {

        ParameterExpression keeperArg = Expression.Parameter(typeof(SecretKeeper), "keeper"); // SecretKeeper keeper argument

        Expression secretAccessor = Expression.Field(keeperArg, "_secret"); // keeper._secret

        var lambda = Expression.Lambda<Func<SecretKeeper, int>>(secretAccessor, keeperArg);

        var func = lambda.Compile(); // Получается функция return result = keeper._secret;

        return func(keeper);

    }

}

public class Program

{

    public static void Main()

    {

        var keeper = new SecretKeeper{Secret = 42};

        Console.WriteLine(keeper.GetSecretUsingExpressionTrees());

    }

}