Using LINQ with System.Reflection Classes

ysw — Sat, 06 Oct 2007 22:54:00 GMT

C# 3.0 and LINQ is not only about accessing data in relational databases and LINQ queries can be used against in-memory data structures as well. Yesterday I had to discover all methods in an assembly satisfying some criteria. As I as playing with Visual Studio 2008 Beta 2 I tried to use new language features everywhere (well, even where it was unnecessary).

I used Linq to filter my classes and methods and wrote this code in a functional style as I am not familiar with LINQ query syntax in C# 3.0.

public IEnumerable<Action> LocateActions()
{
    return GetType().Assembly.GetTypes()
     .Where(v => v.GetCustomAttributes(
            typeof(ActionContainerAttribute), true).Length > 0)
     .SelectMany(v => v.GetMethods(BindingFlags.Public |
                                         BindingFlags.Instance))
     .Where(v => v.GetCustomAttributes(
            typeof(ActionAttribute), true).Length > 0)
     .Select(v => new Action(v));
}

My first version works fine for me; I created the second and third versions just to see what is the most readable. So, the second version of the same method is C# 2.0:

public IEnumerable<Action> LocateActions2()
{
    foreach (Type t in GetType().Assembly.GetTypes())
    {
        if (t.GetCustomAttributes(
                     typeof(ActionContainerAttribute), true).Length > 0)
        {
            foreach (MethodInfo mi in t.GetMethods(BindingFlags.Public |
                                                 BindingFlags.Instance))
            {
                if (mi.GetCustomAttributes(typeof(ActionAttribute),
                                                        true).Length > 0)
                {
                    yield return new Action(mi);
                }
            }
        }
    }
}

and I got the last one from C# 2.0 code.

public IEnumerable<Action> LocateActions3()
{
return
   from t in GetType().Assembly.GetTypes()
   where
      t.GetCustomAttributes(typeof(ActionContainerAttribute),true).Length> 0
      from mi in t.GetMethods(BindingFlags.Public | BindingFlags.Instance)
      where
          mi.GetCustomAttributes(typeof(ActionAttribute), true).Length > 0
        select
          new Action(mi);
    }
}

The first one remains for me the most clear and easy to read, but I believe that not everyone will agree with me.

Which one is the easiest to read for you?

It Could Be Done! : Orcas

Using LINQ with System.Reflection Classes