From: Austin Ziegler <austin@...>
Date: 2002-11-27T23:14:10+09:00
Subject: Re: each_with_index & collect_with_index?

On Wed, 27 Nov 2002 14:51:41 +0900, Alan Chen wrote:
> On Wed, Nov 27, 2002 at 01:49:10PM +0900,
> dblack@candle.superlink.net wrote:
>> So a new global of that kind probably isn't on the horizon. I was
>> playing around with extending objects during iteration, so that
>> you could do:
>> 
>> ary.map {|e| puts "We're at iteration #{e.iteration}"}
>> 
>> or something -- but I haven't come up with a way to do it that
>> fits more than a subset of cases. For one thing, you can't extend
>> Fixnums, so anything based on that method won't work if your
>> array contains those. Also, the syntax of block parameters makes
>> it hard: if you have
>> 
>> ary.map {|e,f,g| ... }
>> 
>> I'm not sure there's a way to determine which object got the
>> #iteration method added to it....
> Well, how about something like Regexp.last_match, where you can
> make a call to retrieve the iteration data.
> 
> ary.map { |e,f,g|
>   ei = Enumerable.iteration_info
>   #...
> }

I like that, sort of. It still has the problem that a global does;
why not make it an importable method for Enumerable?

ary.map { |e, f, g|
  ei = ary.iteration_info
  #...
}

This doesn't work in cases where the same Enumerable could be
iterated more than once (either by Threading or by nesting), but I
think that those are pathological cases anyway.

-austin
-- Austin Ziegler, austin@halostatue.ca on 2002.11.27 at 09.11.52