"Improve your code with dependency injection" code samples

application_controller.rb

class ApplicationController < ActionController::Base
  private

  def app
    APP
  end
end

complex_produce_search.rb

class ComplexProduceSearch
  def initialize(dependencies)
    # Now this can search even vegetables!
    @type = dependencies.fetch(:type)
  end

  def results(args)
    @params = args.fetch(:params)
    @scope  = args.fetch(:scope, :all)

    type.public_send(scope).where(orm_friendly_params)
  end

  private
    attr_reader :type, :params, :scope

    def orm_friendly_params
      # lots of complex logic
    end
end

fruit_app.rb

class FruitApp
  def fruit_search
    ComplexProduceSearch.new(
      type: Fruit,
    )
  end

  def vegetable_search
    ComplexProduceSearch.new(
      type: Vegetable,
    )
  end

  # Potentially one method per controller action
end

APP = FruitApp.new

fruits_controller.rb

class FruitsController < ApplicationController
  def in_season_search
    @results = app.fruit_search.call(
      scope:  :in_season,
      params: params,
    )
  end
end