Multiple inheritance in Lua

multi.lua

local Mom   = {}
local Dad   = {}
local Child = {}

function Mom:work()
  print "I'm a particle physicist!"
end

function Dad:work()
  print "I'm a computer guy!"
end

local parents  = { Mom, Dad }
local rawset   = rawset
local cache_mt = {}
function cache_mt:__index(key)
  for i = 1, #parents do
    local parent = parents[i]

    local value = parent[key]
    if value ~= nil then
      rawset(self, key, value)
      return value
    end
  end
end

local cache = setmetatable({}, cache_mt)
setmetatable(Child, { __index = cache })

Child:work()
Child:work()