class Program
{
    static void Main(string[] args)
    {
        var instance = new Program();
        var cat = new AssemblyCatalog(typeof(Program).Assembly);
        var container = new CompositionContainer(cat);
        container.ComposeParts(instance);
 
        foreach (var plug in instance.Plugins)
        {
            foreach (var category in plug.Metadata.Categories)
            {
                Console.ForegroundColor = ConsoleColor.Yellow;
                Console.Write("{0}, ", category);
                Console.ResetColor();
            }
            Console.WriteLine(string.Empty);
            plug.Value.Write();
        }
        Console.ReadLine();
    }
 
    [ImportMany]
    public Lazy<IPlug, IMetadataView>[] Plugins { get; private set; }
}
 
public enum Category
{
    Travel, Game, City, News
}
 
//[InheritedExport] // do not use inherited export (for some reason it don't working well with metadata)
public interface IPlug
{
    void Write();
}
 
public interface IMetadataView
{
    Category[] Categories { get; }
}
 
[MetadataAttribute]
[AttributeUsage(AttributeTargets.Class, AllowMultiple = true)]
public class CategoryAttribute : Attribute
{
    public CategoryAttribute(Category category)
    {
        Categories = category;
    }
    public Category Categories { get; private set; }
}
 
[Export(typeof(IPlug))]
[ExportMetadata("Categories", Category.Travel, IsMultiple = true)]  // using untyped metadata considered as bad practice
[ExportMetadata("Categories", Category.City, IsMultiple = true)]    // using untyped metadata considered as bad practice
public class NewYork : IPlug
{
    public void Write() { Console.WriteLine("New York"); }
}
 
[Export(typeof(IPlug))]
[Category(Category.Game)]
[Category(Category.News)]
public class Football : IPlug
{
    public void Write() { Console.WriteLine("Football"); }
}