addmethod.lua

local checkArg = checkArg or function(pos, value, ...)
	local exp = {...}
	for _, tp in pairs(exp) do
		if type(value) == tp then
			return
		end
	end
	if #exp == 1 then
		exp = exp[1]
	elseif #exp == 2 then
		exp = table.concat(exp, " or ")
	elseif #exp > 2 then
		exp = table.concat(exp, ", ", 1, #exp - 1) .. ", or " .. exp[#exp]
	end
	error("bad argument #" .. pos .. ": " .. exp .. " expected, got " .. type(value))
end

return function(class, name, func, doc)
	checkArg(1, class, "table")
	checkArg(2, name, "string")
	checkArg(3, func, "function")
	checkArg(4, doc, "string", "nil")
	local method = setmetatable({},{
		__call = function(self, ...)
			return func(...)
		end,
		__tostring = function(self)
			return doc
		end,
		__index = method
	})
	class[name] = method
end