How can i access the value of a local variable from within an expression tree

Question

By examining an expression tree i can get the value of a constant, instance field and property but not a local variable defined in a method.

Executing the following will output 1, 2, 3 (from the constant, instance field and property) then an exception as i don't know how to get the instance on which the FieldInfo is declared in order to call GetValue() for the local variable.

using System;
using System.Linq.Expressions;
using System.Reflection;

namespace Example
{
    class Program
    {
        private int _intField = 2;

        static void Main()
        {
            new Program().Run();
            Console.ReadLine();
        }

        private void Run()
        {
            IntProp = 3;
            var intVariable = 4;
            Test(() => 1);
            Test(() => _intField);
            Test(() => IntProp);
            Test(() => intVariable);
        }

        public int IntProp { get; set; }

        void Test<T>(Expression<Func<T>> func)
        {
            var body = func.Body;

            if (body.NodeType == ExpressionType.Constant)
            {
                Console.WriteLine(((ConstantExpression)body).Value);
            }
            else
            {
                var memberExpression = body as MemberExpression;

                var @object = memberExpression.Member.DeclaringType == GetType()
                    ? this
                    : null; //Can I do anything here? Instance of the method the variable is defined in?

                if (memberExpression.Member.MemberType == MemberTypes.Field)
                {
                    Console.WriteLine(((FieldInfo)memberExpression.Member).GetValue(@object));
                }
                else if (memberExpression.Member.MemberType == MemberTypes.Property)
                {
                    Console.WriteLine(((PropertyInfo)memberExpression.Member).GetValue(@object));
                }
            }
        }
    }
}

Answer 1

The local variable which has been captured by the lambda and included in the expression tree, will at that time really be a field on some compiler-generated class. This works on my version of .NET:

void Test<T>(Expression<Func<T>> func)
{
  var body = func.Body;

  if (body.NodeType == ExpressionType.Constant)
  {
    Console.WriteLine(((ConstantExpression)body).Value);
  }
  else
  {
    var memberExpression = (MemberExpression)body;

    var @object = 
      ((ConstantExpression)(memberExpression.Expression)).Value; //HERE!

    if (memberExpression.Member.MemberType == MemberTypes.Field)
    {
      Console.WriteLine(((FieldInfo)memberExpression.Member).GetValue(@object));
    }
    else if (memberExpression.Member.MemberType == MemberTypes.Property)
    {
      Console.WriteLine(((PropertyInfo)memberExpression.Member).GetValue(@object));
    }
  }
}

Of course, you can also "cheat":

void Test<T>(Expression<Func<T>> func)
{
  Console.WriteLine(func.Compile()());
}