C#

public class ComboBoxItem 
{
  object tag = null;
  string text = null;
  
  public ComboBoxItem(string text)
  {
    this.text = text;
  }
  public object Tag {get {return tag;} set {tag = value;}}
  
  public override string ToString(){return text;}
}

comboBox1.Items.Add( new ComboBoxItem("some text"));

object tag = ((ComboBoxItem) comboBox1.Items[i]).Tag; //note cast. [edit] oops made a mistake, correct now :)[/edit]

public class R
{
        public R(){a=10;b=56;}
	int a, b;
	public int A{
		get{return a;}
		set{a = value;}}
	public int B
	{
		get{return b;}
		set{b = value;}
	}
}

public class Col: CollectionBase 
{
	public Col(){}
	public virtual void Add(R valueT)
	{
		this.List.Add(valueT);
	}
// ...
}

public MyItem this[int i] 
{
  get {return (MyItem) base.List[i];}
  set {base.List[i] = value;}
}

<br />
UserControl control = (UserControl)Page.LoadControl("Components/UserControl.ascx");<br><br />
Type t1 = control.GetType();<br><br />
// you can discover members and methods supported by t1 thanks to reflection :<br><br />
// .MemberInfo<br><br />
// .MethodInfo<br><br />
// ...<br><br />

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