Re: Re: Scripting Systems

Brian Hook wrote:
> It also might be possible to hack Lua so that assignments to 
> undeclared variables generate compile time errors, but I'm not 
> familiar enough with Lua innards to know if that would be easy or 
> difficult.

You can do that without "hacking" lua. This is from the top of my head, 
but if you want to follow this direction I can provide a more detailed 
explanation, or you may also ask on the lua mailing list for more info. 
I think that was a frequently asked question and is probably on the FAQ.


-- Catch access to undeclared properties of the given table.
function CatchUndeclared( table )
	local meta = getmetatable( table )
	if not meta then
		meta = {}
		setmetatable( table, meta )
	end
	meta.__newindex = function (self, key, value)
		error( "cannot add '"..tostring(key).."', '"..tostring(value).."' to 
protected table" )	
	end
end

Whis this function you can protect the given table, so that no new keys 
can be added to it:

table = {
	key1 = 1
}
table.key2 = 2

CatchUndeclared( table )

table.key1 = 2
table.key2 = 3
table.key3 = 4		-- this is not valid!


This also applies to the global table:

CatchUndeclared( _G )

table = {}
newtable = {}		-- this is not valid!


Hope that helps.


-- 
Ignacio Castaño
[email protected]


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