Code for the Dependency Injection (https://docs.google.com/presentation/d/1YuOOdaitw3jcA_QoB7Xp1kCznnAg_Z6dg6R-XI53Ifs/edit?usp=sharing)

app.rb

# frozen_string_literal: true

require 'dry-container'

module DiTalk
  module Services
    class ClassicGreeter
      def greet(name)
        "Hello #{name}"
      end
    end

    class NewEraGreeter
      def greet(name)
        "'s up, #{name}"
      end
    end

    class Container
      extend Dry::Container::Mixin

      register(:greeter, memoize: true) do
        ClassicGreeter.new
      end
    end
  end

  module Controllers
    class Greeter

      def initialize(container)
        @greeter = container.resolve(:greeter)
      end

      def call(env)
        [200, {}, [@greeter.greet('WeWork')]]
      end
    end
  end
end

config.ru

# frozen_string_literal: true

require_relative 'app'

container = DiTalk::Services::Container

run DiTalk::Controllers::Greeter.new(container)

Gemfile

# frozen_string_literal: true

source "https://rubygems.org"

git_source(:github) {|repo_name| "https://github.com/#{repo_name}" }

gem 'rack'
gem 'dry-container'
gem 'minitest'
gem 'mocha'