From: "David A. Black" <dblack@...>
Date: 2005-07-08T22:54:56+09:00
Subject: Re: accessing index inside map

Hi --

On Fri, 8 Jul 2005, Robert Klemme wrote:

> 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.

I'm not a stickler for symmetry (my slogan for Ruby is "The triumph of
balance over symmetry" :-) but it does seem a little arbitrary to have
it recognized that #each_with_index is important for arrays, and #map
is important, but #map_with_index isn't.  (I emphasize "arrays"; I've
never seen a case where it was needed or useful for hashes.)  I don't
think there's any implication that you'd have to have *_with_index.
Nor any demand: I've never seen anyone implement #find_with_index
(what exactly would it do? :-) but I've seen many of
Array#each_with_index.


David

-- 
David A. Black
dblack@wobblini.net