A nonsensical example of what I want to do. Someone please fill in the blanks.

parser_plugin.rb

module Parser
  @formats = {}

  class << self
    attr_accessor :formats

    def create(format)
      formats[format].new
    end
  end

  class Base
    def self.inherited(subclass)
      format = subclass.to_s.split('::').last.downcase.to_sym
      Parser.formats[format] = subclass
    end
  end
end

class Parser::Html < Parser::Base
end

class Parser::Pdf < Parser::Base
end

parser = Parser.create(type: :html)

parser.class

yeah, that's helpful.