From: David Milne <djomilne@...>
Date: 2004-01-09T01:46:41+09:00
Subject: Re: I don't understand this behavour, is it a bug?


"Mark J. Reed" <markjreed@mail.com> wrote in message
news:20040108160145.GB2444@mulan.thereeds.org...
> 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

Thanks  very much Peter and Mark. I got the business about the pointers and
the clone method. I had been starting to feel real uptight :-)

David