ebus.rb

class EventBus
  def initialize
    @map = {}  # kind => [block]
  end

  def signal(kind, *args)
    if blocks = @map[kind]
      blocks.each {|block|
        block.call(*args) rescue nil
      }
    end
  end

  def call(kind, *args)
    if blocks = @map[kind]
      blocks.first.call(*args)
    else
      raise "slot not connected"
    end
  end

  def connect(kind, &block)
    if blocks = @map[kind]
      blocks << block
    else
      @map[kind] = [block]
    end
  end
end


if $0 == __FILE__

  $ebus = EventBus.new

  class StorageService
    def initialize
      @db = {}
      $ebus.connect(:set, &method(:set))
      $ebus.connect(:get, &method(:get))
    end

    def set(key, value)
      @db[key] = value
    end

    def get(key)
      @db[key]
    end
  end

  storage = StorageService.new

  $ebus.signal(:set, "key", "value")
  p $ebus.call(:get, "key")  #=> value

end