From: Robert Klemme <bob.news@...>
Date: 2005-07-08T22:35:47+09:00
Subject: Re: accessing index inside map

Michael Campbell wrote:
> On 7/8/05, David A. Black <dblack@wobblini.net> wrote:
>> Hi --
>
>> I'd still like to see #man_with_index added to Enumerable.
>
> "index" implies an ordering, which maps by definition don't have.
> Shouldn't that be something along the lines of "#map_with_key"?
>
> But point taken; it seems a natural thing, regardless of actual name,
> to be in Enumerable.

Key is ambiguous with Hashes...  Apart from that: I'm not really sure
whether I like that idea.  The basic property of an Enumerable is that it
can be enumerated with each.  There are no guarantees about order etc.
each_with_index is really only there to simplify counting.  If you want
map_with_index then you'd probably have to provide inject_with_index,
find_with_index etc.  Personally I think that map_with_index is rarely
used to justify adding this to the std lib.  Just my 0.02 EUR of course.

Btw, another variant for mapping with index:

enum.inject([]) {|ar,el| ar << ([0,3].include?(ar.size) ? el : el*2) }

Kind regards

    robert