From: Gary Wright <gwtmp01@...>
Date: 2009-07-24T01:00:05+09:00
Subject: Re: How to get real reference to an object?


On Jul 23, 2009, at 10:25 AM, Pavel Smerk wrote:
>
>> You're (almost) always dealing in references in Ruby. (And the almost
>> part doesn't affect you much anyway.) Every reference is exactly one
>> step away from the object; there's no such thing as a reference to a
>> reference. It's very different from Perl in that respect.
>
> Mhm, an unfortunate difference, I'm afraid...
>
> [...]
>>> Morover, why the return value of the assignment is not an l-value?  
>>> The following is legal in Perl ($x ||= 1) *= 2 --- why it is not  
>>> legal in Ruby as well?
>> I assume it's because (x ||= 1) evaluates to the object 1, and 1 *= 2
>> doesn't make sense.
>
> I know, my question is, why it does not evaluate to x. Then it would  
> have the same value (the value of x) and moreover it could stand on  
> the left side of an another assignment (as the x *= 2 does make  
> sense).

It doesn't evaluate to x because Ruby isn't Perl.  It isn't like there  
is an absolute right or wrong way to design a language. Each language  
has its own idioms and techniques, some of which are not translatable  
from one language to the next.

> $ ruby -e 'h = { :a => { :b => "hi" } }; tmp = h[:a][:b]; tmp << "  
> there"; p h'
> {:a=>{:b=>"hi there"}}
>
> which is OK, but not for Float:
>
> $ ruby -e 'h = { :a => { :b => 5.0 } }; tmp = h[:a][:b]; tmp += 5.0;  
> p h'
> {:a=>{:b=>5.0}}
>
> And that's why I'm asking for a "real" reference, because tmp  
> apparently is not any kind of reference to the h[:a][:b].

Variables in Ruby hold references to objects.  They are not labels for  
memory where values are stored. Your example should be written as:

	h[:a][:b] += 5.0

Gary Wright