C# and Expression Trees example

I was just taking a look to the powerful Expression Trees framework in the .NET Framework and I decided to create an example. The result: something that I will never use and I don’t recommend you, but in some way it’s illustrative.

It’s very common to use a class with properties to access the configuration. In this way, you benefit from the static check at compile time, assuming you are in a static language like C#. You can avoid the use of the same string in many places of the code and instead, you use a property like this:

public class AppConf
{
  public static string SomeKey
  {
    get { return ConfigurationManager.AppSettings["SomeKey"]; }
  }
}

Console.WriteLine("AppConf.SomeKey :- {0}", AppConf.SomeKey);

But still, there is a string, and while the string can be moved to a constant what if we want to avoid it? One possible solution is:

public class ExpAppConf
{
  public static string SomeKey
  {
    get
    {
      return ConfigurationManager.AppSettings[
        (new Func<Expression<Func<ExpAppConf, object>>, string>(
          delegate(Expression<Func<ExpAppConf, object>> exp)
          {
            return ((MemberExpression)exp.Body).Member.Name;
          })).Invoke(x => ExpAppConf.SomeKey)];
    }
  }
}

Console.WriteLine("ExpAppConf.SomeKey :- {0}", ExpAppConf.SomeKey);

I’m using Expression Trees, Lambda Expressions and Anonymous Methods, but don’t worry, if you understand all the “trivial-tree paragraph” MVVM blog post out there, you will be fine here.

Which do you think are the possible drawbacks?