public class MPigeon
{
public string Name { get; set; }
}

public void Swap(object a,object b)
{
  object temp=a;
  a=b;
  b=temp;
}

private void button2_Click(object sender, EventArgs e)
{
  MPigeon a = new MPigeon() { Name = "Black" };
  MPigeon b = new MPigeon() { Name = "White" };
  Swap(a, b);
  string ResultMsg = string.Format("a:{0},b:{1}", a.Name, b.Name);
  MessageBox.Show(ResultMsg);
}

public void Swap2(object a, object b)
{
  ((MPigeon)a).Name = "Ronaldo";
  ((MPigeon)b).Name = "Rivaldo";
}