From: "Mark J. Reed" <markjreed@...>
Date: 2004-01-09T01:06:43+09:00
Subject: Re: I don't understand this behavour, is it a bug?

On Fri, Jan 09, 2004 at 12:28:38AM +0900, David Milne wrote:
> Please I wonder if any one can give me some advice?
> 
> I thought I would get into Ruby by "writing BASIC scripts  in Ruby". I
> thought I would try to write one script fragment each day.
> My latest script fragment has a behavour which I do not understand. Is it a
> bug?

> I give variable one a value of [1, 2, 3, 4, 5] . I then set variables two
> and three equal to variable one. I then do stuff to three using one to give
> three the value [1, 3, 6, 10, 15]. My little scrip then prints out variables
> one, two and three. I am amazed to find that one and two appear in the
> printout to have altered them selves to look like three, that is one == two
> == three == [1, 3, 6, 10, 15].

No, it's not a bug.  In Ruby and most OO languages, variables don't
contain the actual objects; they contain references or pointers to the
objects.  So when you make an assignment, the reference is copied, but it's
still referencing the same actual object.  You wind up with multiple variables
pointing to the same object.

If you want to make a duplicate of an object, you have to do so explicitly
by calling the clone method, e.g.

        one = [1, 2, 3, 4, 5]
        two = one.clone
        three = one.clone

-Mark