Implementation registry in lua

registry.lua

local Registry = {} do
Registry.__index = Registry

function Registry:new()
  return setmetatable({_r = {0}}, {__index = self})
end

function Registry:ref(value)
  local registry = self._r

  local ref = self._r[1]
  if ref == 0 then
    self._r[#self._r + 1] = value
    return #self._r
  end

  self._r[1] = self._r[ref]
  self._r[ref] = value

  return ref
end

function Registry:unref(ref)
  self._r[ref] = self._r[1]
  self._r[1] = ref
end

function Registry:get(ref)
  return self._r[ref]
end

function Registry:get_unref(ref)
  local value = self._r[ref]
  self:unref(ref)
  return value
end

end

return Registry