From: Simon Strandgaard <neoneye@...>
Date: 2003-11-25T04:27:13+09:00
Subject: Re: [ann] iterator 0.1

On Tue, 25 Nov 2003 02:39:34 +0900, T. Onoma wrote:

> On Monday 24 November 2003 05:42 pm, Simon Strandgaard wrote:
>> > If Ryby's native iterators (yield+each) ain't flexible enough,
>> > you may want to try using this collection of bidirectional
>> > iterator classes.  Building custom iterator classes are simple.
>> > This is a simple implementation of GoF iterator-pattern.
>>
>> BTW: who has tried this package?  what do you think?
> 
> I haven't tried but I've been eyeing it -- wanting to see what it can do. Can 
> you show some good examples? Or point us to a good place to see some?

There are a, yet small, collection of samples; here:
http://rubyforge.org/cgi-bin/viewcvs/cgi/viewcvs.cgi/projects/iterator/samples/?cvsroot=aeditor

Also my regexp-engine are using it (so far only in the 'iterator' branch):
http://rubyforge.org/cgi-bin/viewcvs/cgi/viewcvs.cgi/projects/regexp_engine/source/?cvsroot=aeditor&only_with_tag=iterator


Ruby's block concept has enormous power. The following examples 
can be implemented even simpler by using block.

Where the difference lies are that Ruby's has internal-iterators,
and this package provides external-iterators.

At some point Ruby's iterator primitives are not sufficiently, Then you
have to use external-iterators.  In my case I am working on a regexp
engine, which I want to take a wide range of different input (ascii,
utf-8, jis, ucs-4..etc). 

If you want flexibility you might consider using external-iterators.

--
Simon Strandgaard



# demonstration of how to make an implicit iterator (fibonacci)
require 'iterator'
class FibonacciIterator < Iterator::Base
  def initialize
    super()
    first
  end
  def first 
    @value = 1 
    @value_next = 1 
  end
  def next 
    tmp, @value = @value, @value_next
    @value_next += tmp
  end
  def is_done?; false end  # infinity
  def current; @value end
end
i = FibonacciIterator.new
p Array.copy_n(i, 10)  #=> [1, 1, 2, 3, 5, 8, 13, 21, 34, 55]
i.close





# demonstration of how to use #transform
require 'iterator'
input = "heLLo woRLD".split(//)
i1 = input.create_iterator
i2 = input.create_iterator_end
dest = []
result = dest.create_iterator_end
Iterator::Algorithm.transform(i1, i2, result) {|val| val.upcase}
p dest.join   #=>  "HELLO WORLD"