From: Trans <transfire@...>
Date: 2008-10-02T03:38:13+09:00
Subject: Re: Mode method for Array



On Oct 1, 12:17 pm, "David A. Black" <dbl...@rubypal.com> wrote:
> Hi --
>
>
>
> On Thu, 2 Oct 2008, Robert Klemme wrote:
> > 2008/10/1 David A. Black <dbl...@rubypal.com>:
> >>> In that case #map might be more appropriate - at least if the target
> >>> collection is an Array.  Btw, did we ever discuss having #map accept a
> >>> parameter which defaults to []?  i.e.
>
> >>> module Enumerable
> >>>  def map(target = [])
> >>>   each {|x| target << yield x}
> >>>   target
> >>>  end
> >>> end
>
> >> I don't think it's a good idea; it generalizes the idea of a mapping
> >> of a collection beyond anything that really seems to me to be a
> >> mapping. If I saw:
>
> >>  [1,2,3,4,5]   =>  "Hi."
>
> >> I would not just say it's a weird mapping; I would not be able to
> >> identify it as a mapping at all. It's a more general transformation.
>
> > I'm not sure I understand exactly what you mean.  My point was simply
> > to allow the caller to provide the target collection where something
> > is mapped to.  Of course you can then also use a String or anything
> > else that supports << (a stream for example) which I find quite neat.
> > But where does "=>" syntax come into play?
>
> It doesn't; I'm just using it to separate the collection and a
> potential "mapping".
>
>    [1,2,3,4,5].map("") {...}   # Result:  "Hi."
>
> I don't think that << correctly represents the concept of mapping, so
> I would not want map to be generalized to any <<-capable target
> object. It's more a <<'ing, or something, than a mapping. It happens
> that the current behavior of map can be implemented using << and an
> empty array, but I don't think that means that << per se is at the
> heart of mapping.

Why not? Building up a collection requires some means of "building
up", and #<< is that means. Standardizing around that method allows
for a more comprehensible and flexible system. Is it a semantic thing
for you? Would it help to think of #collect, instead of #map?

In any case, Robert's idea had to do with providing an initial
collection with which to build, whether #<< is used to do that or not.

T.