1:  class Program
   2:  {
   3:      static void Main(string[] args)
   4:      {
   5:          var instance = new Program();
   6:          var cat = new AssemblyCatalog(typeof(Program).Assembly);
   7:          var container = new CompositionContainer(cat);
   8:          container.ComposeParts(instance);
   9:   
  10:          foreach (var plug in instance.Plugins)
  11:          {
  12:              foreach (var category in plug.Metadata.Categories)
  13:              {
  14:                  Console.ForegroundColor = ConsoleColor.Yellow;
  15:                  Console.Write("{0}, ", category);
  16:                  Console.ResetColor();
  17:              }
  18:              Console.WriteLine(string.Empty);
  19:              plug.Value.Write();
  20:          }
  21:          Console.ReadLine();
  22:      }
  23:   
  24:      [ImportMany]
  25:      public Lazy<IPlug, IMetadataView>[] Plugins { get; private set; }
  26:  }
  27:   
  28:  public enum Category
  29:  {
  30:      Travel, Game, City, News
  31:  }
  32:   
  33:  //[InheritedExport] // do not use inherited export (for some reason it don't working well with metadata)
  34:  public interface IPlug
  35:  {
  36:      void Write();
  37:  }
  38:   
  39:  public interface IMetadataView
  40:  {
  41:      Category[] Categories { get; }
  42:  }
  43:   
  44:  [MetadataAttribute]
  45:  [AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
  46:  public class CategoryAttribute : Attribute
  47:  {
  48:      public CategoryAttribute(Category category)
  49:      {
  50:          Categories = category;
  51:      }
  52:      public Category Categories { get; private set; }
  53:  }
  54:   
  55:  [Export(typeof(IPlug))]
  56:  [ExportMetadata("Categories", Category.Travel, IsMultiple = true)]  // using untyped metadata considered as bad practice
  57:  [ExportMetadata("Categories", Category.City, IsMultiple = true)]    // using untyped metadata considered as bad practice
  58:  public class NewYork : IPlug
  59:  {
  60:      public void Write() { Console.WriteLine("New York"); }
  61:  }
  62:   
  63:  [Export(typeof(IPlug))]
  64:  [Category(Category.Game)]
  65:  [Category(Category.News)]
  66:  public class Football : IPlug
  67:  {
  68:      public void Write() { Console.WriteLine("Football"); }
  69:  }