Factory.sequence :email do |n|
    "person#{n}@example.com"
  end

  Factory.sequence(:email, ['angela', 'brett', 'alec']) do |name|
    "#{name}@example.com"
  end

>> Factory.next :email
=> "angela@example.com"
>> Factory.next :email
=> "brett@example.com"
>> Factory.next :email
=> "alec@example.com"
>> Factory.next :email
=> "angela@example.com"
>> Factory.next :email
=> "brett@example.com"

Factory.sequence(:email, 50..60) do |n|
  "user_#{n}@example.com"
end
 
>> Factory.next :email
=> "user_50@example.com"
>> Factory.next :email
=> "user_51@example.com"
>> Factory.next :email
=> "user_52@example.com"

Factory.sequence(:email, %w[angela brett alec]) do |name,i|
  "#{name}_#{i}@example.com"
end
 
>> Factory.next :email
=> "angela_0@example.com"
>> Factory.next :email
=> "brett_1@example.com"
>> Factory.next :email
=> "alec_2@example.com"
>> Factory.next :email
=> "angela_3@example.com"
>> Factory.next :email
=> "brett_4@example.com"

Factory.sequence(:name, %w[angela brett alec hal debbie tracey jared]) do |name,i|
  "#{name}_#{i}"
end
 
Factory.sequence(:domain, %w[something.com example.com mydomain.com]) do |domain|
  domain
end
 
Factory.define(:email_address) do |f|
  f.address { "#{Factory.next(:name)}@#{Factory.next(:domain)}" }
end
 
>> 20.times { ea = Factory.build :email_address; puts ea.address }
angela_0@something.com
brett_1@example.com
alec_2@mydomain.com
hal_3@something.com
debbie_4@example.com
tracey_5@mydomain.com
jared_6@something.com
angela_7@example.com
brett_8@mydomain.com
alec_9@something.com
hal_10@example.com
debbie_11@mydomain.com
tracey_12@something.com
jared_13@example.com
angela_14@mydomain.com
brett_15@something.com
alec_16@example.com
hal_17@mydomain.com
debbie_18@something.com
tracey_19@example.com

>> Factory.reset :name
>> Factory.next :name
=> "angela_0"

class Factory
  def self.sequence(sequence_name, enum = nil, &blk)
    @@sequences ||= {}
 
    enum = enum.to_a
 
    @@sequences[sequence_name] = {
      :enum => enum,
      :index => 0,
      :infinite_counter => 0,
      :template  => blk
    }
  end
 
  def self.next(sequence_name)
    seq = @@sequences[sequence_name]
 
    retval = case seq[:template].arity
      when 1
        seq[:template].call(seq[:enum][seq[:index]])
      when 2
        seq[:template].call(seq[:enum][seq[:index]], seq[:infinite_counter])
    end
 
    seq[:index] = (seq[:index]+1 == seq[:enum].size) ? 0 : seq[:index]+1
    seq[:infinite_counter] += 1
    @@sequences[sequence_name] = seq
    retval
  end
 
  def self.reset(sequence_name)
    @@sequences[sequence_name][:index] = 0
    @@sequences[sequence_name][:infinite_counter] = 0
  end
end