From: "David A. Black" <dblack@...>
Date: 2005-07-11T20:07:37+09:00
Subject: Re: accessing index inside map

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Hi --

On Mon, 11 Jul 2005, Yukihiro Matsumoto wrote:

> Hi,
>
> In message "Re: accessing index inside map"
>    on Mon, 11 Jul 2005 10:50:31 +0900, "Pe=F1a, Botp" <botp@delmonte-phil=
=2Ecom> writes:
>
> |#  (1..6).each_with_index.map{|x,i|[2,5].include?(i) ? x : x*2}
> |#
> |#then.  It's much simpler isn't it?
>
> |but isn't
> |    each_with_index.map
> |
> |so close to being
> |    map_with_index
> |
> |?
>
> Yes.  But when we add map_with_index, we might be asked to add
> collect_with_index, detect_with_index, inject_with_index, and all
> other enumerable methods _with_index as well.

I'm probably the person who has asked for map_with_index the most, and
I promise not to ask for *_with_index :-)

I can understand that a general solution makes sense, though I'm still
very unclear on the whole notion of "index" as it pertains to
Enumerable.

As for:

   (1..6).each_with_index.map{|x,i|[2,5].include?(i) ? x : x*2}

it is simpler than enum_for, but I wonder if it's equally clear.  It
seems that one would have to memorize a list of methods that behave
this way, rather than really seeing it directly in the code.  Also,
would one have to define, say, #each to return an Enumerator, if one
were writing a new class and mixing in Enumerable?


David

--=20
David A. Black
dblack@wobblini.net
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