From: "trans.  (T. Onoma)" <transami@...>
Date: 2004-09-22T03:58:08+09:00
Subject: Re: Array#index block and rdetect

On Tuesday 21 September 2004 10:28 am, Yukihiro Matsumoto wrote:
> Hi,
>
> In message "Re: Array#index block and rdetect"
>
>     on Tue, 21 Sep 2004 20:33:52 +0900, "trans.  (T. Onoma)" 
<transami@runbox.com> writes:
> |For sake of interchangeability (after all that's the upside of ducktyping)
> |have an alias for both:
>
> Arrays have number index, and hashes have arbitrary type of keys, so
> that there should hardly be the case of need for interchangeability
> between them.  Do you have any example of the usage?

Well, like anything of this sort one doesn't have examples off hand b/c this 
can't be done currently --one ends up doing them other ways. Same goes for 
ordered hashes. I've run into a need for them many times, but find alternate 
solutions b/c they are not available. So I have no ready use cases of them 
either, but I know they can be useful.

Just the same I put together a simple example to give a taste. It shows how 
one general method might do the job, rather then having special cases. It is 
given below.

> Currently, I'd rather feel that it's good to avoid the term "index"
> for hashes, for example, renaming IndexError to KeyError for Hash
> class.

I go both ways. I think interchangeable parts are good --it goes along with 
the ideas of duck types. But sometimes it is also good for things to be 
different. In this case it might be better b/c if hashes ever get order, then 
index will be needed for that, not key. So yes on this I agree with you but 
only if order will eventually be usable for hashes. Otherwise interchangeable 
is more useful.

# SIMPLE DEMO
  
  play_list = [ 'i never was cool', 'SEA CHANGE', 'Shepherd Moons' ]
  artists = { 'i never was cool' => 'anna wolfe', 'SEA CHANGE' => 'Beck', 
'Shepherd Moons' => 'Enya' }
  
  def show(x)
    x.each_with_index{|v,i|
      puts "#{i} => #{v.upcase}"
    }
  end

#=begin  # remove first '#' to deactivate section
  
  # Not Interchangeable  
   
  puts "\nMy Play List"
  show(play_list)
  puts "\nArtist Reference"
  show(artists)
  puts "\nArtists In Order of Play"
  show(play_list.collect {|n| artists[n] })
  puts
 
=begin
  in `show': undefined method `upcase' for ["Shepherd Moons", "Enya"]:Array 
(NoMethodError)
=end

  # Interchangable  
  
  class Hash
    def each_with_index
      each_pair{|k,v| yield(v,k)}
    end
  end

  puts "\nMy Play List"
  show(play_list)
  puts "\nArtist Reference"
  show(artists)
  puts "\nArtists In Order of Play"
  show(play_list.collect {|n| artists[n] })
  puts
  
=begin 

  My Play List
  0 => I NEVER WAS COOL
  1 => SEA CHANGE
  2 => SHEPHERD MOONS
  
  Artist Reference
  Shepherd Moons => ENYA
  SEA CHANGE => BECK
  i never was cool => ANNA WOLFE
  
  Artists In Order of Play
  0 => ANNA WOLFE
  1 => BECK
  2 => ENYA
  
=end


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 //    trans.
/ \    transami@runbox.com

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