how to handle # operator for proxy tables?

[Valerio Schiavoni <valerio.schiavoni@...>]

hello,
i use proxy tables to catch modifications on 1st elements of a table:

proxytable = function ( orig )
	return setmetatable({},
		{
		__index=orig,
		__newindex=function(t,k,v)
				rawset(orig,k,v);
					if (k==1) then
						print("do something")
					end
				end,
		__len=function(t) return #orig end,
		__pairs = function(t) return pairs(orig)end })
		end
		
t={1,2,3,4}
print(#t)
t=proxytable(t)
print(#t)

The problem is that the i was expecting the 2nd call to #t to return 0.
How can I get around this?

It seems Lua5.2 will handle this:
http://www.batbytes.com/luafaq/#T8.2.5, but for now I'm stuck with
5.1.4.

Thanks
Valerio