Csharp/C Sharp by API/System/AttributeUsage

AttributeUsage(AttributeTargets)

using System;
[AttributeUsage(AttributeTargets.Class)]
public class RandomSupplier : Attribute
{
  public RandomSupplier()
  {
  }
}
[AttributeUsage(AttributeTargets.Method )]
public class RandomMethod : Attribute
{
  public RandomMethod()
  {
  }
}
[RandomSupplier]
public class OriginalRandom
{
  [RandomMethod]
  public int GetRandom()
  {
    return 5;
  }
}
using System;
[RandomSupplier]
public class NewRandom
{
  [RandomMethod]
  public int ImprovedRandom()
  {
    Random r = new Random();
    return r.Next(1, 100);
  }
}
public class AnotherClass
{
  public int NotRandom()
  {
    return 1;
  }
}
using System;
using System.Reflection;
class MainClass 
{
  public static void Main(string[] args) 
  {
    RandomSupplier rs;
    RandomMethod rm;
    foreach(string s in args)
    {
      Assembly a = Assembly.LoadFrom(s);
      foreach(Type t in a.GetTypes())
      {
        rs = (RandomSupplier) Attribute.GetCustomAttribute(
         t, typeof(RandomSupplier));
        if(rs != null)
        {
          Console.WriteLine("Found RandomSupplier class {0} in {1}",
           t, s);
          foreach(MethodInfo m in t.GetMethods())
          {
            rm = (RandomMethod) Attribute.GetCustomAttribute(
             m, typeof(RandomMethod));
            if(rm != null)
            {
              Console.WriteLine("Found RandomMethod method {0}"
               , m.Name );
            }
          }        
        }
      }
    }
  }
}