Re: protecting exported data from within C

[Romulo Bahiense <romulo@...>]

> However, I find I can still modify the value of Account.version. I only 
> get the error message
> if I try and add new fields to the table.  From the description in the
> book my function should
> be called whenever lua tries to assign something to the table.

	No. The __newindex metamethod will be called if, and only if, there are 
no corresponding value in the respective table.

	To avoid such behavior, you could create a table for the __index 
metamethod which will hold read-only values, and create a function for 
the __newindex metamethod that will check if the value already exists in 
the __index table.


The __newindex function would be something like:

__newindex = function (obj,key,value)
	local meta = getmetatable(obj)

	if type(meta)~='table' or type(meta.__index)~='table' then
		return
	end

	if rawget(meta.__index,key)~=nil then
		error('Attempt to override "'..tostring(key).. '" - a constant value')
	else
		rawset(obj,key,value) -- Adds it to the table.
	end
end

--rb