A pattern to keep the core small, adding features by having a plugin system. Define a module called Plugins, store future plugins in a module-level instance variable.

Register plugin is adding the plugin name and module to the @plugins hash. Load plugin by looking up if the plugin exists in @plugins hash.

module Plugins
  PluginNotFoundError = Class.new(StandardError)
  @plugins = {}

  def self.register_plugin(name, modudle)
    @plugins[name] = modudle
  end

  def self.load_plugin(name)
    plugins_cache = @plugins
    if plugin != plugins_cache[name]
      require "plugins/#{name}"
      raise PluginNotFoundError, "Plugin #{name} did not register correctly." unless plugin = plugins_cache[name]
    end
    plugin
  end
end

Replace @plugins = {} to a thread-safe cache to ensure thread safety.

@plugins = Cache.new