From: Simon Strandgaard <none@...>
Date: 2003-10-08T16:27:58+09:00
Subject: Re: map/collect iterating over multiple arrays/arguments

Zoran Lazarevic <zoranlazarevic@yahoo.com> skrev i en
nyhedsmeddelelse:32c0bb6a.0310071950.55c75dd0@posting.google.com...
> Simon Strandgaard wrote in message news:...
> > On Mon, 06 Oct 2003 17:17:55 -0700, Zoran Lazarevic wrote:
> > > Can I iterate over multiple arrays/collections?
> > > Are there Iterators for enumerables, like in Java?
> >
> > Yes I have made some iterator classes.. But its not yet released.
> >
>
> Simon, the iterator class uses indexing ( @data[@position] ) and that
> is exactly what I tried to avoid. This does NOT work for collections
> that do not support indexing operator[] (e.g. linked lists, iterating
> through SQL resultset, etc.)

You can write an implicit iterator, like this:

server> cat snippet_implicit.rb
require 'iterator'
class ImplicitIterator < Iterator::Base
  def initialize
    super()
    first
  end
  def first; @value = 0 end
  def next; @value += 1 end
  def is_done?; @value >= 10 end
  def current; @value end
end
i = ImplicitIterator.new
until i.is_done?
  p i.current
  i.next
end
server> ruby snippet_implicit.rb
0
1
2
3
4
5
6
7
8
9
server>

Is this better ?  :-)


> Apparently it is not possible to iterate using Collection.each over
> multiple collections. It is possible by using one thread per
> collection, but I do not want to go there.

You can make an iterator which can iterate over multiple iterators at
the same time, like this:

require 'iterator'
class MultiIterator < Iterator::Base
  def initialize(*iterators)
    @iterators = iterators
    first
  end
  def first; @iterators.each{|i| i.first} end
  def next; @iterators.each{|i| i.next} end
  def is_done?
    @iterators.each{|i| return true if i.is_done? }
    false
  end
  def current; @iterators end
end

a = %w(a b c d e).create_iterator
b = (0..4).to_a.create_iterator
i = MultiIterator.new(a, b)
until i.is_done?
  ia, ib = i.current
  p [ia.current, ib.current]
  i.next
end

Is this better ? ...  I hope ;-)


--
Simon Strandgaard