Publish-subscribe pattern implementation in Lua (ported from "Learning JavaScript Design Patterns" book)

pubsub.lua

-- https://addyosmani.com/resources/essentialjsdesignpatterns/book/#observerpatternjavascript

local M = {}

-- Storage for topics that can be broadcast
-- or listened to
local topics = {}

-- A topic identifier
local sub_uid = 0

-- Publish or broadcast events of interest
-- with a specific topic name and arguments
-- such as the data to pass along
M.publish = function(topic, args)
  if not topics[topic] then
    return false
  end

  local subscribers = topics[topic]
  local len = subscribers and #subscribers or 0

  while len > 0 do
    subscribers[len].func(topic, args)
    len = len - 1
  end
end

-- Subscribe to events of interest
-- with a specific topic name and a
-- callback function, to be executed
-- when the topic/event is observed
M.subscribe = function(topic, func)
  if not topics[topic] then
    topics[topic] = {}
  end

  sub_uid = sub_uid + 1

  table.insert(topics[topic], {
    token = sub_uid,
    func = func
  })

  return sub_uid
end

-- Unsubscribe from a specific
-- topic, based on a tokenized reference
-- to the subscription
M.unsubscribe = function(token)
  for k, v in pairs(topics) do
    for i = 1, #v do
      if v[i].token == token then
        table.remove(v, i)
        return token
      end
    end
  end
end

return M