Module:No globals

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This is a meta module.

This module is meant to be used only by other modules. It should not be invoked in wikitext.

This module prevents the use of global variables within Scribunto modules, in order to avoid creating bugs that are difficult to track down. When using this module, an error will be thrown if any nil global is read or if any global is written to, with the exception of arg. The arg variable is excluded because it is necessary for Scribunto's require function to work properly.

Usage

Place require('Module:No globals') at the top of the module using it.

This module was adapted from Module:No globals on Wikipedia.
Adaptation is noted for reference and attribution only. This module may differ from the original in function or in usage.

The above documentation is transcluded from Module:No globals/doc. (edit | history)
Editors can experiment in this module's sandbox (create | mirror) and testcases (create) pages.
Subpages of this module.

local mt = getmetatable(_G) or {}
function mt.__index (t, k)
	if k ~= 'name' and 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)