From: daz <dooby@...10.karoo.co.uk>
Date: 2005-11-12T11:57:14+09:00
Subject: Re: Function Variable and Return Value References


Eric Hofreiter wrote:

> The question is, how exactly does ruby behave in this respect?
> I haven't quite figured out what the rules are.

FAQ [4.5: How are arguments passed?]
http://www.rubygarden.org/faq/entry/show/27


> It appears that Fixnum and basically every user-made object are
> always passed by value, and can not reference each other.

The rules of assignment apply (ref FAQ).

>
> However, arrays seem to be passed into functions by reference,
> and returned by value, though the objects they contain are copied.

That's a bit of a muddle (if I might be so bold ;).

>
> At first, I thought variables were always pointers, and things
> such as a = b meant that if you change a, you change b.

a and b now reference the same object -- that's right.

> It seems now that this is in fact never the case.

Oh, no :)

> So that brings me to my second question: what are the purpose of
> the methods dup and clone?  I thought they would be useful if
> you needed to assign copies rather references, but it seems that
> objects are copied by default when assigned.

There's no copying on assignment - that's the same reason you
may need dup/clone.
I can usually manage to get most of the way through a prog without
resorting to dup/clone by using the feature that many methods
return a modified object (a modified copy of the target).

>
> Can someone please explain this to me?

I'm not very chatty but the above might get you started.


daz