From: Mike Stok <mike@...>
Date: 2001-11-30T23:24:36+09:00
Subject: [ruby-talk:27068] Re: Using Enumerable

On Fri, 30 Nov 2001, Peter Hickman wrote:

> Thanks to all who replied, like all ruby it was alot simpler than I
> thought.
>
> class Fred
>         include Enumerable
>
>         def initialize
>                 @end = 10
>                 @pointer = 0
>         end
>
>         def each
>                 while @pointer != @end do
>                         @pointer += 1
>                         yield @pointer
>                 end
>                 @pointer = 0
>         end
> end

Be careful that the use of an instance variable means that you may be
surprised by the behaviour of code like

  fred = Fred.new

  fred.each { |f1|
      puts "f1 is #{f1}"
      fred.each { |f2|
          puts "f2 is #{f2}"
      }
  }

as the two iterators "share" @pointer and don't play well together.  Using
code like

  def each
      0.upto(@end) { |pointer|
          yield pointer
      }
  end

allows the iterators to be independent of each other.

Mike

-- 
mike@stok.co.uk                    |           The "`Stok' disclaimers" apply.
http://www.stok.co.uk/~mike/       | GPG PGP Key      1024D/059913DA
mike@starnix.com                   | Fingerprint      0570 71CD 6790 7C28 3D60
http://www.starnix.com/            |                  75D2 9EC4 C1C0 0599 13DA