Lua - 扩展用户数据

Question

我有一个带metatable的userdata值，我想添加另一个metatable：

local obj = Game:create_object() --Obj now contains userdaa
print(obj:get_x()) --Use method in metatable of obj

--I would like to do something like this:
local mt = {name = "test"}
mt.__index = mt
setmetatable(obj, mt)
print(obj.name)

--And still have the methods from the beginning
print(obj:get_x())

这有可能吗？如果没有，有哪些替代方案？

Answer 1

local obj = Game:create_object() --Obj now contains userdaa
print(obj:get_x()) --Use method in metatable of obj

local new_fields = {name = "test"}
local mt = {}
for k, v in pairs(getmetatable(obj)) do
   mt[k] = v
end
new_fields.__index = mt.__index
mt.__index = setmetatable(new_fields, new_fields)
setmetatable(obj, mt)

--And still have the methods from the beginning
print(obj.name)
print(obj:get_x())