A simple, alternative class system for Lua

classes.lua

return function(name)
	local class = require(name)
	local classmt = getmetatable(class)
	if getmetatable(class) == nil then
		local props = {unpack(class)}
		for i = #class, 1, -1 do
			class[i] = nil
		end
		local classmt = {}
		local instancemt = {__index = class}
		function classmt:__call(...)
			local instance = {}
			for i, property in ipairs(props) do
				local value = select(i, ...)
				instance[property] = value
			end
			return setmetatable(instance, instancemt)
		end
		function instancemt:__tostring()
			local parts = {name .. '('}
			for i, property in ipairs(props) do
				parts[#parts + 1] = tostring(self[property])
				parts[#parts + 1] = ', '
			end
			if #props > 0 then
				parts[#parts] = ')'
			else
				parts[#parts + 1] = ')'
			end
			return table.concat(parts)
		end
		setmetatable(class, classmt)
	end
	return class
end

test.lua

local getclass = require 'classes'

local vector = getclass 'vector'

print(vector(2, 7))
local v1 = vector(1, 1)
v1:add(vector(-10, -6))
print(v1)

vector.lua

local vector = {'x', 'y'}

function vector:add(vec)
    self.x = self.x + vec.x
    self.y = self.y + vec.y
end

return vector