using System;

using System.Linq.Expressions;

​

public class Program

{

    public static void Main(string[] args)

    {

        ParameterExpression param = Expression.Parameter(typeof(Test), "obj");

        Expression a = Expression.Property(param, "A");

        Expression b = Expression.Property(param, "B");

        Expression result = CustomCombine(a, b);

​

        var lambda = Expression.Lambda<Func<Test, int>>(result, new ParameterExpression[] { param });

        Func<Test, int> func = lambda.Compile();

​

        var obj = new Test();

        var val = func(obj);

​

        Console.WriteLine("Result is " + val);

​

    }

​

    private static Expression CustomCombine(Expression a, Expression b)

    {

        var variable = Expression.Variable(a.Type, "cached");

        var aVal = Expression.Assign(variable, a);

​

        var mult = Expression.Multiply(variable, b);

        var result = Expression.Add(mult, variable);

        // here we are making Block with variable declaration and assigment

        var block = Expression.Block(new ParameterExpression[]{variable}, aVal, result);

        return block;

    }

}

​

public class Test

{

    public int A

    {

        get

        {

            Console.WriteLine("Property A is accessed");

            return 42;

        }

    }

​

    public int B

    {

        get

        {

            return 1;

        }

    }

}