From: Jason Creighton <androflux@...>
Date: 2003-06-14T07:58:34+09:00
Subject: Re: does each work on a copy?

On Fri, 13 Jun 2003 10:42:55 +0200
"Robert Klemme" <bob.news@gmx.net> wrote:

> 
> "Jason Creighton" <androflux@remove.to.reply.softhome.net> schrieb im
> Newsbeitrag
> news:20030612123014.33a6449b.androflux@remove.to.reply.softhome.net...
> > On Thu, 12 Jun 2003 23:14:37 +0900
> > Rasputin <rasputin@shrike.mine.nu> wrote:
> >
> > > > remember that pretty much everything is a reference and you won't go
> far
> > > > wrong
> > >
> > > I thought so, until this happened!
> > > The array was full of references, so I thought el held the
> > > reference from the Array.
> > >
> > > It seems to hold a copy of the reference...
> >
> > No, it doesn't. When you do a:
> 
> Sorry, but in fact you're wrong.  The reference is copied indeed.

It looked as if the OP thought that 'word' was a "copy" (ie, object.dup), not
a
reference to the same object in the Array. Sorry, I could have phrased that
better.

> > a = "Hello world, nice to meet you!".split(' ')
> > a.each { |word| word = "lala" }
> > p a
> > ["Hello", "world,", "nice", "to", "meet", "you!"]
> >
> > You're binding word to a different object, not changing the objects
> themselves.
> 
> Binding "word" to another object is indeed done by copying the reference
> to the other object.  Or in other terms, after this assignment there is
> one more reference to the object.

Right: We're not modifing whatever objects were "in" (In the sense that the
Array contains references to objects) the Array: We're creating a new object
("lala") and making word refer to that object. Had we done a word.upcase!,
that would have modified the object in the array.

> a="foo" # one ref to "foo"
> b=b # two refs to "foo"
> a=nil # one ref to "foo"
> b=nil # zero refs to "foo"
> 
> I think you did want to say the right thing but mixed up terms a little.

Obviously. :-)

> Maybe Perl has contributed to the confusion since it in fact does some
> aliasing of references in arrays on function invocations the allow a
> function to change array element references directly by simply assigning.
> IMHO the ruby way is much cleaner and easier to understand.

Once you get used to it: I had used Python before, which basically does the
same thing as Ruby, so it wasn't a big shock for me.

Jason Creighton