I remember the first perl project I was paid for. I needed HoH, LoH, HoL, etc. I read perldsc, and after a few hours of reading and experimenting, I understood it pretty well and got on with my work. Because I was new at it, a few subtle bugs surfaced later during testing, but that happens whenever you learn something new.
in reply to Maintainable Code?
Noone who goes through this continues to think HoH should be avoided because it is "too advanced".
Try to get your co-worker on a small task where he will be encouraged (forced) by the nature of the task to learn it.