create_user_from_invitation.rb

class CreateUserFromInvitation
  include Waterfall
  
  def initialize(invitation)
    @invitation = invitation
  end
  
  def call
    chain { build_user }
    when_falsy { user.save }
      .dam { user.errors }
    chain { UserMailer.affiliate_welcome(user).deliver_later }
  end
  
  private
  attr_reader :user
  
  def build_user
    @user = #logic to build user goes here
  end
end