Rolling back changes (cont'd)

Solution:

 1   class UserDB
 2     def adduser(username, password, address, phone)
 3       rollback = []
 4       begin
 5         @phone_db.adduser(username, address, phone)
 6         rollback.push proc { @phone_db.deluser(username) }
 7         @system1_db.adduser(username, password)
 8         rollback.push proc { @system1_db.deluser(username) }
 9         @system2_db.adduser(username, password)
10         rollback.clear
11       ensure
12         rollback.reverse_each { |p| p.call }
13       end
14     end
15   end