Decorator pattern

gistfile1.cs

public interface Abstraction
{
  void Proc();
}

public class Impl1 : Abstraction
{
  public void Proc()
  {
  }
}

public class Impl2 : Abstraction
{
  public Impl2(Abstraction inner)
  {
    _inner = inner;
  }

  public void Proc()
  {
    // do some extra stuff
    _inner.Proc();
  }
}