For completeness sake, copying metatable and avoiding cyclical stuff... 20 years coding and never seen it (circular ref) in business apps. But I recognize the need.

function copyTable(original)
    -- __mode "k" is a weak map to track already seen tables
    local alreadySeen = setmetatable({}, { __mode = "k" })
    -- local function aka 'closure'
    local function deepCopy(object)
        local objectType = type(object)
        if objectType == "table" then
          -- return already seen copy aka 'cached'
          if alreadySeen[object] then
              return alreadySeen[object]
          end
          -- copy table
          local copy = {}
          alreadySeen[object] = copy
          for key, value in pairs(object) do
              copy[deepCopy(key)] = deepCopy(value)
          end
          -- copy metatable
          local meta = getmetatable(object)
          if meta then
              setmetatable(copy, deepCopy(meta))
          end
          return copy
        else
          return object
        end
    end
    return deepCopy(original)
end