service object syntax

class RegisterUser
  def self.call(*args, &block)
    new(*args, &block).execute
  end
  def initialize(user)
    @user = user
  end
  def execute
    # old code
  end
  # private methods
end

RegisterUser.call(user)

class RegisterUser
  def initialize(user)
    @user = user
  end
  def execute
    # old code
  end
  # private methods
end

RegisterUser.new(user).execute