1_coupled.rb

# Bad because the dependency on ModelClass and ApiClass are hard-coded

module HitTheApi
  def self.go
    ids_to_update = ModelClass.what_ids_should_I_update
    
    ids_to_update.each do |id|
      data = ApiClass.fetch_me_data(id)
      ModelClass.persist_data(id, data)
    end
  end
end

1a_refactored.rb

# Cleaner 'go' method, but now the dependencies are hard-coded and pushed deeper. Worse.

module HitTheApi
  def self.go
    ids_to_update.each do |id|
      fetch_and_persist(id)
    end
  end
  
  private
  
  def self.ids_to_update
    ModelClass.what_ids_should_I_update
  end
  
  def self.fetch_and_persist(id)
    data = ApiClass.fetch_me_data(id)
    ModelClass.persist_data(id, data)
  end
end

2_deps_passed.rb

# Deps passed in makes things easy to test

module HitTheApi
  def self.go(model, api)
    ids_to_update = model.what_ids_should_I_update

    ids_to_update.each do |id|
      data = api.fetch_me_data(id)
      model.persist_data(id, data)
    end
  end
end

2a_refactored.rb

# If the 'go' method needs to do something more complex, breaking out private methods starts to be painful

module HitTheApi
  def self.go(model, api)
    ids_to_update(model).each do |id|
      fetch_and_persist(api, model, id)
    end
  end
  
  private
  
  def self.ids_to_update(model)
    model.what_ids_should_I_update
  end
  
  def self.fetch_and_persist(api, model, id)
    data = api.fetch_me_data(id)
    model.persist_data(id, data)
  end
end

3_classy.rb

# Similar to 2, but now you're instantiating something for no conceptual reason 
# or any real benefit to the code

module HitTheApi
  def initialize(model, api)
    @model = model
    @api = api
  end

  def go
    ids_to_update = @model.what_ids_should_I_update
    
    ids_to_update.each do |id|
      data = @api.fetch_me_data(id)
      @model.persist_data(id, data)
    end
  end
end

3a_refactored.rb

# Retains 2's testability but without 2a's ugly internal methods, but pushing the use of 
# instance variables down into internal methods feels bad.

module HitTheApi
  def initialize(model, api)
    @model = model
    @api = api
  end

  def go
    ids_to_update.each do |id|
      fetch_and_persist(id)
    end
  end

  private

  def ids_to_update
    @model.what_ids_should_I_update
  end

  def fetch_and_persist(id)
    data = @api.fetch_me_data(id)
    @model.persist_data(id, data)
  end
end

4_setter_injection.rb

module HitTheApi
  attr_writer :api_getter, :model_getter

  def go
    ids_to_update.each do |id|
      fetch_and_persist(id)
    end
  end

  private

  def ids_to_update
    model.what_ids_should_I_update
  end

  def fetch_and_persist(id)
    data = api.fetch_me_data(id)
    model.persist_data(id, data)
  end

  def api
    @api ||= api_getter.call
  end

  def api_getter
    @api_getter ||= ApiClass.public_method(:new)
  end

  def model
    @model ||= model_getter.call
  end

  def model_getter
    @model_getter ||= ModelClass.public_method(:new)
  end
end

methods.rb

module HitTheApi
  def self.go
    ids_to_update = model_class.what_ids_should_I_update
    
    ids_to_update.each do |id|
      data = api_class.fetch_me_data(id)
      model_class.persist_data(id, data)
    end
  end

  def self.model_class
    ModelClass
  end

  def self.api_class
    ApiClass
  end
end