Module:No globals

This module is subject to page protection. It is a highly visible module in use by a very large number of pages, or is substituted very frequently. Because vandalism or mistakes would affect many pages, and even trivial editing might cause substantial load on the servers, it is protected from editing.

This module causes an error if any nil global is read or if any global is written to, with the exception of arg. To use, add

require('Module:No globals')

to the top of the module using it. The arg variable is excluded because it is necessary for Scribunto's require function to work properly. (See the Scribunto source code here.)

local mt = getmetatable(_G) or {}
local oldIndex = mt.__index or function() return nil end
mt.__index = function(t, k)
	if k ~= 'name' and k ~= 'arg' then
		error('Tried to read nil global ' .. tostring(k), 2)
	end
	return oldIndex(t, k)
end
local oldNewindex = mt.__newindex or rawset
function mt.__newindex(t, k, v)
	if k ~= 'name' and k ~= 'arg' then
		error('Tried to write global ' .. tostring(k), 2)
	end
	oldNewindex(t, k, v)
end
setmetatable(_G, mt)