From: Robert Klemme <bob.news@...>
Date: 2004-09-20T23:04:45+09:00
Subject: Re: Array#index block and rdetect


"trans. (T. Onoma)" <transami@runbox.com> schrieb im Newsbeitrag
news:200409200947.47623.transami@runbox.com...
> On Monday 20 September 2004 08:54 am, Robert Klemme wrote:
> > In my understanding Enumerable#each_with_index just goes through the
> > enumerable and counts an index which can be used for printing or
counting
> > or whatever. So I would not change this method. These indexes are
purely
> > per enumeration and can change for any number of reasons.
>
> That's an interesting perspective. So you're saying index is just a
"helper"
> counter. These being equivalent:
>
>   enumobj.each_with_index {|a,i| ... }
>
>   enumobj.each {|a| i=(i||-1)+1; ... }

I'd say rather

i=-1
enumobj.each {|a| i+=1; ... }

Reason: scoping rules:

>> %w{aa bb cc}.each {|a| i=(i||-1)+1; p [a,i]}
["aa", 0]
["bb", 0]
["cc", 0]
=> ["aa", "bb", "cc"]

> Maybe so, although I'd prefer #each_with_counter, in that case. Think of
an
> "index" in the back of a book.

Well, there might be better names, but the current name happens to be the
one it is.  I fear there's enough potential for confusion in that matter
so I wouldn't necessarily change that name.

> A bit of an aside, I've been thinking about synchronizing enumerable
objects.

Please be careful with the term "synchronize" - this is usually
interpreted in the context of concurrency (multiple threads).

> For the sake of discussion lets say *=* means synchronize. So,
>
>   ([1,2,3]*=*[7,8,9]).each {|a,b| puts "#{a},#{b}" }
>
>   => 1,7
>      2,8
>      3,9
>
> Then "indexing" can also be done with
>
>   (enumobj*=*(0..enumobj.length-1)).each{|a,i|}
>
> If a method #range is defined, this can be simplified too
>
>   (enumobj*=*enumobj.range).each{|a,i|}
>
> Is there a good way to do this?

>> [1,2,3].zip [7,8,9]
=> [[1, 7], [2, 8], [3, 9]]

    robert