Why was the object_id for true and nil changed in ruby2.0?

ruby-talk
1

irb(main):001:0> true.object_id
=> 20
irb(main):002:0> false.object_id
=> 0
irb(main):003:0> nil.object_id
=> 8

The values for true and nil were respectively 2, 4 in 1.9.3 and 1.8.7,
but have been changed to 20, 8 in ruby2.0.0 - even though the id of
false remains the same i.e. 0 and the ids for Fixnum maintains the same
old 2n+1 pattern.

What's the reason behind this object_id change?

Why was this change made? How is this going to help developers?

The full question can be seen here:

thanks!

···

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2

your question was already answered at stackoverflow:

Seems to be something to do with “flonums” – a technique for speeding up

floating point calculations on 64-bit:
github.com/ruby/ruby/blob/v2_0_0_0/include/ruby/ruby.h#L383-431 and
ruby-forum.com/topic/4404164.

···

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3

hm the forumtopic i linked was in english ...

hm okay, Flonums may be not the reason because they are only in 2.1dev

  a = 1.1 + 1.2
  b = 1.1 + 1.2
  p(a.object_id == b.object_id)

this shows true on 2.1, its false on 2.0p0

···

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4

Well, there is a new answer on Stack Overflow.

Gentlemen over here might want to take a look:

Seems legit... but I am not sure how can something like this lead to
better perfomance? Any comments?

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5

Hans Mackowiak wrote in post #1102392:

your question was already answered at stackoverflow:

Seems to be something to do with “flonums” – a technique for speeding up

floating point calculations on 64-bit:
github.com/ruby/ruby/blob/v2_0_0_0/include/ruby/ruby.h#L383-431 and
ruby-forum.com/topic/4404164.

I have tried to read it, but the presentations given in that link are
written in Japanese, and I couldn't understand what Flonums are why they
are implemented.

Know any place where I can read them in English to understand why it was
changed?

···

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6

Hans Mackowiak wrote in post #1102451:

hm okay, Flonums may be not the reason because they are only in 2.1dev

  a = 1.1 + 1.2
  b = 1.1 + 1.2
  p(a.object_id == b.object_id)

this shows true on 2.1, its false on 2.0p0

This shows true in my system too, but my ruby -v is ruby 2.0.0p0
(2013-02-24 revision 39474) [x86_64-linux], not 2.1.

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7

Because immediate values have no overhead. It takes memory and cpu cycles
to create an object instance; it takes no (extra) memory if the value is
stored in the reference (ie the object id _is_ the value, albeit slightly
modified), and far fewer cycles to shift and OR some bits.

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Sent from my phone, so excuse the typos.

8

ruby-forum.com/topic/4404164 specifically states why it was changed. Its a speed thing.

···

Bharadwaj Srigiriraju <mailto:lists@ruby-forum.com>
March 20, 2013 10:10 AM

I have tried to read it, but the presentations given in that link are
written in Japanese, and I couldn't understand what Flonums are why they
are implemented.

Know any place where I can read them in English to understand why it was
changed?

Hans Mackowiak <mailto:lists@ruby-forum.com>
March 20, 2013 2:03 AM
floating point calculations on 64-bit:
github.com/ruby/ruby/blob/v2_0_0_0/include/ruby/ruby.h#L383-431 and
ruby-forum.com/topic/4404164.

--
D. Deryl Downey

  "The bug which you would fright me with I seek" - William Shakespeare - The Winter's Tale, Act III, Scene II - A court of Justice.

9

This only should be true on 64bit Ruby 2.0.

···

On Wed, 20 Mar 2013 17:22:57 +0100, Bharadwaj Srigiriraju <lists@ruby-forum.com> wrote:

Hans Mackowiak wrote in post #1102451:

hm okay, Flonums may be not the reason because they are only in 2.1dev

  a = 1.1 + 1.2
  b = 1.1 + 1.2
  p(a.object_id == b.object_id)

this shows true on 2.1, its false on 2.0p0

This shows true in my system too, but my ruby -v is ruby 2.0.0p0
(2013-02-24 revision 39474) [x86_64-linux], not 2.1.

--
Matma Rex

10

I'm interested (as is Hans, I think) in understanding the specifics of
the implementation and _why_ this leads to better performance. Looks
like someone would have to translate the Japanese, though.

···

On 20 March 2013 14:27, D. Deryl Downey <me@daviddwdowney.com> wrote:

ruby-forum.com/topic/4404164 specifically states why it was changed. Its a speed thing.

11

Bartosz Dziewoński wrote in post #1102469:

···

On Wed, 20 Mar 2013 17:22:57 +0100, Bharadwaj Srigiriraju > <lists@ruby-forum.com> wrote:

(2013-02-24 revision 39474) [x86_64-linux], not 2.1.

This only should be true on 64bit Ruby 2.0.

Yes.

On 32 bit systems the object_id didn't change at all.

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