Window = {}Window.prototype = {x = 0, y = 0, width = 70, height = 100}Window.mt = {}function Window.new(o)    setmetatable(o, Window.mt)    return oend--[[Window.mt.__index = function (table, key)    return Window.prototype[key]end--]]Window.mt.__index = Window.prototype--当我们想不通过调用__index metamethod来访问一个表，我们可以使用rawget函数，w = Window.new{x = 10, y = 20}print(w.width)