From: Xavier Noria <fxn@...>
Date: 2010-11-13T00:18:08+09:00
Subject: Re: what's an object?

On Fri, Nov 12, 2010 at 3:56 PM, Robert Dober <robert.dober@gmail.com> wrote:

> That's actually what I meant: When passing the parameter the diagram
> is correct. I do not see any reason why you claim the diagram
> incorrect - for what the param passing semantics concerns - only
> because Ruby gives you the freedom to reassign the param inside the
> body of the method.

You think the parameter is an alias, and the local variable masks it
right? As if usage was pass-by-value but you couldn't tell because of
that formality. Isn't that convoluted? The spec says local variables
are created, why do you think a second local variable is later created?

> I wanted to express that this manipulation should not be used to prove
> the correctness or incorectness of a given param passing model.
> Clearer?

I am not familiar with MRI but I'd swear this is what implements the
argument value copying of pass-by-value semantics (that's from
vm_insnhelper.c in 1.9.2):

	/* copy arguments */
	for (i=0; i < (sp - rsp); i++) {
	    p_rsp[i] = rsp[i];
	}

There, rsp has type VALUE*. If I understand the code correctly, that
in turn comes from copying the VALUEs in the argv argument of
vm_call0(). They are all plain assignments, we are just copying
pointers (or immediate values).