Transparent shallow copy of tables

["Stuart P.Bentley" <stuart@...>]

How can I do a shallow copy of a table that operates identically to the 
original? Currently I'm setting tables to be empty tables with metatables 
that save deletions and create similar shallow copies on index access, but 
this is causing problems with functions like table.concat().

I'd prefer to avoid a deep copy if possible, since that would take a long 
time regardless of access depth.

My current approach is online at 
http://bazaar.launchpad.net/~stuart/sandpad/stuart/annotate/head%3A/sandpad.wlua.