An example of differing ways of abstracting initialization into the parent

a_ too_much_in_the_parent_the_wrong_way.rb

class AbstractScraper
  def initialize(username, password)
    @agent = WWW::Mechanize.new
    @agent.user_agent_alias = "Windows Mozilla"
    @agent.keep_alive = false
    login(username, password)
  end
end

class NormalAScraper < AbstractScraper
  
end

class NormalBScraper < AbstractScraper
  
end

class GoofyScraper < AbstractScraper
  def initialize
    @agent = WWW::Mechanize.new
    @agent.user_agent_alias = "Windows Mozilla"
    @agent.keep_alive = false
    login
  end
end

b_better_composition.rb

class AbstractScraper
  def initialize(username, password)
    initialize_agent
    login(username, password)
  end

  def initialize_agent
    @agent = WWW::Mechanize.new
    @agent.user_agent_alias = "Windows Mozilla"
    @agent.keep_alive = false
  end
end

class NormalAScraper < AbstractScraper
  
end

class NormalBScraper < AbstractScraper
  
end

class GoofyScraper < AbstractScraper
  def initialize
    initialize_agent
    login
  end
end

c_that_and_each_class_init_is_more_obvious_imo.rb

class AbstractScraper
  def initialize_agent
    @agent = WWW::Mechanize.new
    @agent.user_agent_alias = "Windows Mozilla"
    @agent.keep_alive = false
  end
end

class NormalAScraper < AbstractScraper
  def initialize(username, password)
    initialize_agent
    login(username, password)
  end
end

class NormalBScraper < AbstractScraper
    def initialize(username, password)
    initialize_agent
    login(username, password)
  end
end

class GoofyScraper < AbstractScraper
  def initialize
    initialize_agent
    login
  end
end