gistfile1.rb

# A controller
class PostsController < ActionController::Base
  def create
    @context = PostManagementContext.new(params[:posts])
    if @context.save
      # redirect
    end
  end

  def search
    # ...
  end

  # ...
end

# Context class
#
# Could be Context::PostManagement. Whatever now.
class PostManagementContext
  def initialize(params)
    @params = params
  end

  def save
    @post = Post.new(@params)
    if @post.save 
      # @post is probably ActiveRecord, so there's nothing to extend
      @twitter = login_twitter
      @twitter.extend TwitterPoster
      @twitter.post(@post.body)
    end
  end

  def save_comment
    @comment = Comment.new(@params)
    # ... instantiates Model
    if @comment.save 
      @twitter = login_twitter
      @twitter.extend TwitterFollower
      @twitter.follow(@comment.twitter_nickname)
    end
  end

  private

  def login_twitter
    Twitter.new(login: "login", password: "password")
  end
end


# Data object
class Twitter
  def initialize(user) 
    @twitter = Twitter::API.login(user[:login], user[:password]) # fake API class
  end
end

# Roles
module TwitterPoster
  def post(body)
    # calls Twitter API
  end

  def parse_tweet_body
    # ...
  end

  # other methods related to posting on Twitter
end

module TwitterFollower
  def follow(body)
    # calls Twitter API
  end

  # other methods related to following on Twitter
end