### main.rb ###
require './plugin'

Dir['./plugins/*.rb'].each { |f| require f }
Plugin.register_plugins

# Can we send a message to each plugin
Plugin.plugins.each do |plugin|
    plugin.handle_command('test')
end

### plugin.rb ###
require 'set'

class Plugin
    @plugins = Set.new

    def self.plugins
        @plugins
    end

    def self.register_plugins
        Object.constants.each do |klass|
            const = Kernel.const_get(klass)
            if const.respond_to?(:superclass) and const.superclass == Plugin
                @plugins << const
            end
        end
    end
end

### plugins/cat.rb ###
class CatPlugin < Plugin
    def handle_command(cmd)
        puts "Cat got command #{cmd}"
    end
end