Module:No globals

This module is rated as ready for general use. It has reached a mature form and is thought to be bug-free and ready for use wherever appropriate. It is ready to mention on help pages and other Wikipedia resources as an option for new users to learn. To reduce server load and bad output, it should be improved by sandbox testing rather than repeated trial-and-error editing.

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.

Warning:

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Usage

Include this module at the top of your code. An error will be raised any time your code tries to read or write to a non-local (undeclared) variable.

Tests

Module:No globals	success: 1, error: 0, skipped: 0
Module:No globals/sandbox	success: 1, error: 0, skipped: 0

See testcases
Diff sandbox code

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