From: Morton Goldberg <m_goldberg@...>
Date: 2007-09-30T08:19:12+09:00
Subject: Re: a = Dog.new # a is not a pointer and not a reference?

On Sep 29, 2007, at 4:13 PM, Austin Ziegler wrote:

> On 9/29/07, Morton Goldberg <m_goldberg@ameritech.net> wrote:

<snip>

> A variable in Ruby isn't like Java, PHP, C++, C, or even Pascal.
>
>> I think it best to think of a Ruby variable as holding a reference to
>> an object. Ruby's reference semantics are different from C++'s, but
>> IMO more mainstream. C++'s reference semantics are peculiar, to say
>> the least, and perhaps even unique [*]. Ruby's variable semantics are
>> simple and clean when compared to C++, so I recommend forgetting
>> about making such comparisons.

My use of "holding" may be unfortunate. I only meant it conceptually.  
I was trying to make things simple for the OP.

> No, it's best to forget the concept of a Ruby variable as a  
> shoebox. It
> doesn't *hold* anything.
>
> In C/C++, a variable is a shoebox. This shoebox has a physical  
> location
> and dimension (the address in memory). One shoebox can hold the  
> location
> of another shoebox. That's a pointer or a reference (under the covers,
> they are the same in C++).
>
> A variable in Ruby is a sticky note (like a Post-It). You can put that
> sticky note on an object, or you can put multiple sticky notes on an
> object. But if you move the sticky note, you're changing the object to
> which it references. Since they're labels, the sticky notes don't
> contain anything -- they just name the object that they're attached  
> to.
> Since they don't contain anything, no other sticky note can point to
> another sticky note.

By "sticky notes" you seem to be talking about bindings, like a Lisp  
variable makes. That is how I think of Ruby variables, myself, but I  
didn't think bringing bindings up would help the OP. I didn't think  
of the analogy with sticky notes. I like that -- I'll have to  
remember it.

> A Ruby variable is nothing like a C++ variable. Never has been, never
> will be.

We are in complete agreement. That was the point I trying to make.  
Did I phrase it so obscurely that you took me to be saying the opposite?

>> [*] Betrand Meyer of Eiffel fame has often made fun of C++'s  
>> reference
>> semantics. He has claimed they are beyond the understanding of mere
>> mortals. He is joking, of course.

That should be Bertrand not Betrand. Pardon my typo.

> No, he's not. Bjarne is clearly not a mere mortal. Or from the  
> upper planes.

Are you implying Bjarne Stroustrup is some kind of demon? He always  
struck me as a very nice person.

Regards, Morton