From: Matthew Kerwin <lists@...>
Date: 2013-04-15T13:06:52+09:00
Subject: Re: Wondering why no "increment" or "decrement" operator in ruby

tamouse mailing lists wrote in post #1105640:
> On Sun, Apr 14, 2013 at 10:23 PM, Matthew Kerwin <lists@ruby-forum.com>
> wrote:
>> Incidentally, if you're using MRI, because of a clever optimisation your
>> 'a' variable literally holds the value `1`, not a reference per se.
>
> I guess I don't understand this last part; I can still call an
> instance method on a, so it must be more than just a value..., no? As
> I can call an instance method on 1. I guess I don't quite get what you
> mean by 'value'...

In the C code underlying MRI, ruby objects are referred to by integers 
called 'VALUE's, which are effectively references to the instantiated 
objects.  However for fixnums (and the new flonums) the VALUE is 
actually a reversibly-mangled version of the actual value.

Here's a transcript from IRB on my 64 bit Linux box in a recent build of 
trunk:

irb:001> 1.object_id >> 1
=> 1
irb:002> 328.object_id >> 1
=> 328
irb:003> -2.object_id >> 1
=> -2

Because the numeric value is known, there's no need to instantiate a 
"proper" object to encapsulate it; rather the interpreter can look at 
the VALUE, see that it has the "is a Fixnum" bits set, and dispatch the 
appropriate methods through the Fixnum class.

On that point: Fixnum "objects" don't even have a singleton:

irb:004> class << 1; end
TypeError: can't define singleton
  from (irb):4
  from /usr/local/bin/irb21:12:in `<main>'
irb:005> a = 1; def a.foo; end
TypeError: can't define singleton
  from (irb):5
  from /usr/local/bin/irb21:12:in `<main>'

Every method you send to a Fixnum object goes through the class.

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