Iterator pattern

Provides a way to access the elements of an aggregate object sequentially without exposing the underlying representation.

External Iterator - e.g. Java: for (Iterator i = list.iterator(); i.hasNext()} { }

Nice thing about External iterators is that the client is driving.

In Ruby, we use Enumerable elements to be enumerated over must define <=> define each on class to be iterated over.

Q: What happens if the object changes that you're iterating over? A: Maybe take a shallow copy and work on that.

class Account
  attr_accessor :name, :balance

  def initialize(name, balance)
    @name = name
    @balance = balance
  end

  def <=>(other)
    balance <=> other.balance
  end
end

class Portfolio
  include Enumerable

  def initialize()
    @accounts = []
  end

  def each(&block)
    @accounts.each(&block)
  end

  def add_account(account)
    @account << account
  end
end