From: Martin DeMello <martindemello@...>
Date: 2005-10-12T00:21:52+09:00
Subject: Re: multi-dimensional Arrays

Peter v. N. <skull2crush@hotmail.com> wrote:
> 
> I know there exist "simple" ways (Google's thy friend)
> to create md arrays with Ruby. But it's somehow cumbersome
> and it would be nice if it could be done like "array = Array.new(3,3)" 
> -> I know too that this means not the 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 � la
> "int[][] arr = new int[3][3]"?

There are several different kinds of multidimensional arrays. One is
true rectangular arrays (efficient memory allocation, bounds checked in
every dimension) - I think FISh supports those[1], and probably Matlab
as well.

Then there's C's rectangular arrays with weak (no!) bounds checking -
the array is allocated as a contiguous block, and multidimensional
indexes are converted into (computed) single dimensional offsets into
the block.

And finally, Ruby uses the lists-of-lists approach, in which you have
only one-dimensional arrays, but every cell of those arrays can be an
array itself (and so on recursively). Not as efficient as the
rectangular approach, but it allows for irregularly shaped arrays.

martin

[1] http://www-staff.it.uts.edu.au/~cbj/FISh/Announcement/