Undefined value for Luau

undefined.lua

-- Written by R0bl0x10501050

local module = {
	['new'] = function()
		local self = setmetatable({}, {
			__newindex = function()
				error("Cannot set property of undefined")
			end,
			__index = function(tbl, k)
				if k == "DEBUG_CHECK" then
					return true
				else
					error("Cannot retrieve property of undefined")
				end
			end,
			__call = function()
				error("Cannot call undefined")
			end,
			__concat = function()
				error("Cannot concat undefined")
			end,
			__unm = function()
				error("Cannot negate undefined")
			end,
			__add = function()
				error("Cannot add undefined")
			end,
			__sub = function()
				error("Cannot subtract undefined")
			end,
			__mul = function()
				error("Cannot multiply undefined")
			end,
			__div = function()
				error("Cannot divide undefined")
			end,
			__mod = function()
				error("Cannot use undefined in a modulus expression")
			end,
			__pow = function()
				error("Cannot use undefined in an exponent expression")
			end,
			__tostring = function()
				return "[object Undefined]"
			end,
			__eq = function(this, other)
				return true -- Since this will only run if two undefined values are being compared
			end,
			__lt = function()
				error("Cannot compare undefined")
			end,
			__le = function()
				error("Cannot compare undefined")
			end,
			__mode = 'kv',
			__len = function()
				error("Cannot get length of undefined")
			end,
		})
		return self
	end,
	['test'] = function(objA, objB)
		if objA and not objB then return false end
		local isAUndefined, isBUndefined = false, false
		local s, _ = pcall(function()
			return objA['DEBUG_CHECK']
		end)
		if s then
			isAUndefined = true
		end
		local s2, _ = pcall(function()
			return objB['DEBUG_CHECK']
		end)
		if s2 then
			isBUndefined = true
		end
		return (isAUndefined and isBUndefined)
	end,
}

return module