From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-10-11T22:25:53+09:00
Subject: Re: multi-dimensional Arrays

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On Tue, 11 Oct 2005, Peter v. N. wrote:

> Hi all,
>
> I'm a Ruby noob so please forgive me...
>
> I know there exist "simple" ways (Google's thy friend) to create md array=
s
> with Ruby. But it's somehow cumbersome and it would be nice if it could b=
e
> done like "array =3D Array.new(3,3)" -> I know too that this means not th=
e
> same in Ruby...
>
> What I like to know: what led to the decission to do it that way
> and not like it is done in the C/C++ (Java) languages =E0 la
> "int[][] arr =3D new int[3][3]"?

this is precisely because these languages do __not__ have multi-dimensional
arrays and they muse be composed of uni-dimensional ones.  ruby is the same=
=2E
the big difference is that there is no difference between compile time and
runtime in ruby so, if i could say

   a =3D array[3]

in ruby, then

   a =3D array[3][3]

would mean

   a =3D (the_first_array =3D array[3])[ index =3D 3]

in otherwords you'd index the first array by the second value.  another iss=
ue
is that, in ruby, a declaration is the same as a definition.  so, in c, you
cannot write

   printf ("%d\n", (int [42])[0]);

but in ruby you can write

   printf "%d\n", [42][0]

because you can simoultaneously define and declare an object, and this have
object, including array, literals.


> Maybe because this approach is not strictly oo-oriented? But then, switch=
es
> and loops in Ruby are neither.

i thinks it's more syntax/interpreter related.

> It's just the devil inside who likes to know about the philosophy about t=
he
> "why it is done like that" and I'm not bitching about Ruby (by no means).

the best reason may be that's it's so easy to setup you're own md definer:

   harp:~ > cat a.rb
   require 'pp'

   md =3D lambda{|*ds| Array::new(ds.shift||0).map{md[*ds] unless ds.empty?=
}}

   pp md[]
   pp md[1]
   pp md[2]
   pp md[2,3]
   pp md[2,3,4]


   harp:~ > ruby a.rb
   []
   [nil]
   [nil, nil]
   [[nil, nil, nil], [nil, nil, nil]]
   [[[nil, nil, nil, nil], [nil, nil, nil, nil], [nil, nil, nil, nil]],
    [[nil, nil, nil, nil], [nil, nil, nil, nil], [nil, nil, nil, nil]]]


cheers.

-a
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| email :: ara [dot] t [dot] howard [at] noaa [dot] gov
| phone :: 303.497.6469
| Your life dwells amoung the causes of death
| Like a lamp standing in a strong breeze.  --Nagarjuna
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