Rails service definition

example.rb

# A
module Document
  class ActionService
    def initialize(a, b)
      @a = a
      @b = b
    end
    
    def call
      compute
    end
  end
end

# B
module DocumentService
  class Action
    def initialize(a, b)
      @a = a
      @b = b
    end
    
    def call
      compute
    end
  end
end

# C
module DocumentService
  def action(a, b)
    compute
  end
end

# D
class DocumentService
  def self.action(a, b)
    compute
  end
end

# E
module Document
  class ActionService
    class << self
      def call(a, b)
        new(a).call(b)
      end
    end
    
    def initialize(a)
      @a = a
    end
    
    def call(b)
      service_instance.call(b)
    end
    
    def service_instance
      @service_instance ||= ..whatever..
    end
  end
end

# F
module DocumentService
  class Action
    def call(a, b)
      compute
    end
  end
end

# G
module DocumentService
  class Create
    def self.call(a, b)
      compute
    end
    
    private def whatever
    end
  end
end