From: "David A. Black" <dblack@...>
Date: 2007-09-29T20:35:03+09:00
Subject: Re: Noobie question: saving the values

Hi --

On Sat, 29 Sep 2007, Druhie Almighty wrote:

> May you forgive me for this irrelevant thread but nonetheless, I need
> your help.
> I'm new at programming and recently I've faced with the problem
> connected with the peculiarity of Ruby. Unlike many other languages, the
> variables in it contain not the objects themselves but only links to
> them, right?

"Link" isn't the right word. Variables contain either the actual value
of the object, or a reference to the object. It's not that peculiar,
actually :-)

> So can you please explain me why do these two operations very close to
> each other result in different ways, considering the fact that both a
> and b contain the same link?
>
> 1)
> a="13"
> b=a
> a="12"

As soon as you re-assign to a variable, you completely cut the
previous assignment. b is still assigned to "13", but you're now using
a to refer to a completely different object ("12").

> puts b --> 13
>
> 2)
> a="13"
> b=a
> a[1]="2"

Here, you're not assigning a new object to a; rather, you're changing
the object that a refers to. Since b refers to the same object, when
you inspect b you see the change reflected.

> puts b --> 12
>
> To be more exact, in my program I need an array and a
> variable=method(array). But when I call the method, the array itself
> changes as well. How do I save the value of the array and get the
> neccesary value of the variable at the same time?
> P.S. And yes, I sought for solution in a guide but so far haven't found
> anything.

You can 'dup' the array, either before you call it or in the method:

   var = method(array.dup)

Keep in mind, though, that the objects inside the array won't be
duped. You're just creating a new array. So you can add objects to the
new array (or delete objects from it) without affecting the original
array.


David

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