From: Maggie  Xiao <mxiao@...>
Date: 2003-01-30T13:42:36+09:00
Subject: Re: A simple program but strange output

Thank you, guys.
----- Original Message -----
From: "Daniel P. Zepeda" <daniel@zepeda-zone.net>
To: "ruby-talk ML" <ruby-talk@ruby-lang.org>
Sent: Wednesday, January 29, 2003 9:34 PM
Subject: Re: A simple program but strange output


> On Thu, 30 Jan 2003 13:13:43 +0900
> "Maggie  Xiao" <mxiao@ee.ualberta.ca> wrote:
>
> > Hi there,
> >
> > I wrote a simple program to enumerate an array. The code is as below:
> > class Test
> >  def initialize
> >    @x=[0,1,2]
> >    @tem=@x
> >    @y=@x
> >    y=del(@tem)
> >  printf "#{@x}\n"
> >  printf "#{@y}\n"
> >           end
> >   def del(x)
> >  x.delete_at(0)
> >  return x
> >  end
> > end
> > a=Test.new
> >
> > But the output is :
> > 12
> > 12
> > Why  @x and @y are changed? Is there anyone can tell me how to deal with
> > this problem?
>
> Because @tem is a reference (pointer) to the object, which is the array
> [0,1,2], and so is @y. @x,@y and @tem are all pointing to the same Array
> object, they are not different objects.
> If you want different objects, you have to make a copy:
>
> Here's an example using irb:
>
> irb(main):001:0> a = [0,1,2]
> => [0, 1, 2]
> irb(main):002:0> a.id
> => 537808534
> irb(main):003:0> b = a
> => [0, 1, 2]
> irb(main):004:0> b.id
> => 537808534
> irb(main):005:0> c = a.clone
> => [0, 1, 2]
> irb(main):006:0> c.id
> => 538070796
> irb(main):007:0>
>
>
>
>
> >
>
>
> --
> Daniel P. Zepeda
>
>