Sounds like you want Java-style "interfaces" to me.
Follow the thread back. Objective-C had them way first, and their ur-name is "protocols."
D'oh! Sorry, I had read that, but then forgot.
David
-- David Wheeler AIM: dwTheory [EMAIL PROTECTED] ICQ: 15726394 http://kineticode.com/ Yahoo!: dew7e Jabber: [EMAIL PROTECTED] Kineticode. Setting knowledge in motion.[sm]