From: John Park <jcpark@...>
Date: 2008-12-28T19:50:56+09:00
Subject: New to Ruby: copying arrays?

Hi.  First-time poster here.  I've done some programming in Delphi
before (like 10 years ago), and I wanted to get back to programming as a
hobby.  I've looked at several languages, and Ruby looked the funnest.
:)  So here I am.

For my first project, I've decided to make a Sudoku class, making it
general enough so that it can easily be subclassed to implement many
Sudoku variations out there.

To store the board state, I decided to make an instance variable @board
which is a two-dimensional array of 9x9.  And there would be several
methods that will manipulate the board.

Then it occurred to me that it would be nice to have a .revert method
that will revert the board to its initial state.

Easy enough, I thought.

To the .initialize method, I added the line:

@initialboard = @board

and I added a new .revert method which did:

@board = @initialboard

And this, as you Ruby-experts may imagine, is where I came to
face-to-face with Ruby's "variables are references, not containers"
nature.  Every time I manipulated @board, the "content" of @initialboard
would get altered as well, making it useless as a backup of the initial
state of the board.

I've tried .dup and .clone methods, but it didn't work because @board
was a two-dimensional, array-within-array structure.  .dup and .clone
methods only duplicated the top level array, and the sub-level arrays
were still being referenced to the same data, leading to the same result
as the first time around.

So here's my question.  Is there a simple and elegant way to duplicate
the entire content of a multi-dimensional array?

Right now, the only workarounds I can think of are: 1) store the data in
one long one-dimensional array, of 2) use an iterator to duplicate each
sub-level arrays individually.  Neither are very elegant nor attractive.
:(

Thanks in advance to any insight you guys can give me in this matter.



Oh, one more question: what's the difference between .dup and .clone
methods?
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