# Ruby's implementation of Fixnum-assignment

**URL:** <https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549>\
**Category:** Ruby\
**Created:** [December 21, 2009, 4:56pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549 "2009-12-21T16:56:14Z")\
**Posts on this page:** 19\
**Page:** 1

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 4:56pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/1 "2009-12-21T16:56:14Z")

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Hi,

I’ve made the following observations about Ruby’s apparent  
implementation:

1. Integer’s in the range -2 **30 to 2** 30-1 are Fixnum’s. Integers  
outside that range are Bignum’s
2. For Fixnum “i”, i’s object\_id is twice i’s value plus 1. Said  
another way, i’s object\_id is i’'s binary value left-shifted with 1 as  
padding.
3. Object\_id’s of Bignum’s close to the boundaries of Fixnum’s bear no  
apparent relationship to the Fixnum object\_id’s.

These observations suggest to me that an assignment statement like  
“a=1” requires the interpreter to do no more than:

1. Search for the identifier “a” in the current scope.
2. If found, use it; if not, enter it in the current scope and then  
use it.
3. “Use it” means take the binary representation of the assigned  
value, left shift it with “1” padding, and make that current  
object\_id of the identifier “a”.
4. There is no need to locate free space in an memory pool where  
object values for Bignums, Strings and other object are stored. For  
Fixnums, the object\_id IS the value, just a little shifted.

Is my speculation about this aspect of Ruby’s implementation correct,  
or am I all wet?

Thanks in advance for any comments you may wish to offer,  
Richard

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 5:26pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/2 "2009-12-21T17:26:04Z")

</div>

On Dec 21, 2009, at 10:55 AM, RichardOnRails wrote:

> Is my speculation about this aspect of Ruby’s implementation correct,  
> or am I all wet?

Generally correct. You might want to look at  
[http://en.wikipedia.org/wiki/Tagged\_pointer](http://en.wikipedia.org/wiki/Tagged_pointer) for a discussion of this  
overall technique. This technique is one way around ‘boxing’ primitive  
types such as small integers, boolean values, nil, and symbols.

Gary W.

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 5:34pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/3 "2009-12-21T17:34:51Z")

</div>

RichardOnRails:

> 1. Integer’s in the range -2 **30 to 2** 30-1 are  
> Fixnum’s. Integers outside that range are Bignum’s

Depending on the architecture:

> > (2**62-1).class  
> > =\> Fixnum  
> > (2**62).class  
> > =\> Bignum  
> > RUBY\_DESCRIPTION  
> > =\> “ruby 1.9.1p376 (2009-12-07 revision 26041) [x86\_64-linux]”

> 1. For Fixnum “i”, i’s object\_id is twice i’s value plus 1. Said  
> another way, i’s object\_id is i’s binary value left-shifted with  
> 1 as padding.

Right, Fixnums are immediate in Ruby (at least in MRI).

> 1. Object\_id’s of Bignum’s close to the boundaries of Fixnum’s  
> bear no apparent relationship to the Fixnum object\_id’s.

Right, because Bignums are ‘regular’ objects.

> For Fixnums, the object\_id IS the value, just a little shifted.

Spot on.

There was a very nice talk about these things; you might want to google  
for “Understanding Ruby’s Object Model” (the top links do not open for  
me at the moment, so I’m not sure this is the talk I think of).

— Shot

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 6:28pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/4 "2009-12-21T18:28:07Z")

</div>

2009/12/21 RichardOnRails  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> I’ve made the following observations about Ruby’s apparent  
> implementation:
> 
> 1. Integer’s in the range -2 **30 to 2** 30-1 are Fixnum’s. Integers  
> outside that range are Bignum’s
> 2. For Fixnum “i”, i’s object\_id is twice i’s value plus 1. Said  
> another way, i’s object\_id is i’'s binary value left-shifted with 1 as  
> padding.
> 3. Object\_id’s of Bignum’s close to the boundaries of Fixnum’s bear no  
> apparent relationship to the Fixnum object\_id’s.

All correct.

> Fixnums, the object\_id IS the value, just a little shifted.
> 
> Is my speculation about this aspect of Ruby’s implementation correct,  
> or am I all wet?

Hm… While you have many things right, I don’t fully agree. No  
variable (be it a local variable like “a” in your example or an  
instance variable like “@a”) has an object id. Object id is a  
property of an object which might be referenced by many variables.  
Your step 3 actually mixes two separate things: evaluation of the  
expression of the right side of “=” and assignment. “Using” in an  
assignments means to take whatever the expression spits out and store  
it in the variable.

Now, what your right hand expression yields is an object reference.  
For optimization purposes some object references are special in that  
they actually _are_ the object (these are the “immediate values” which  
Gary mentioned, Fixnums for example). This does not make special  
treatment for assignments necessary. Rather, it makes special  
treatment for _method calls_ necessary. Because then the interpreter  
does not have to look up the object on the heap etc.

Someone with more intimate knowledge of the implementation might be  
able to explain this better. But I believe it’s important to point  
out that the difference is not in the assignment but in the right hand  
side expression which - in the case of a Fixnum - yields a special  
object reference.

Kind regards

robert

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 7:55pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/5 "2009-12-21T19:55:55Z")

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On Dec 21, 11:25 am, Gary W. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> On Dec 21, 2009, at 10:55 AM, RichardOnRails wrote:
> 
> > Is my speculation about this aspect of Ruby’s implementation correct,  
> > or am I all wet?
> 
> Generally correct. You might want to look at [http://en.wikipedia.org/wiki/Tagged\_pointer](http://en.wikipedia.org/wiki/Tagged_pointer) for a discussion of this overall technique. This technique is one way around ‘boxing’ primitive types such as small integers, boolean values, nil, and symbols.
> 
> Gary W.

Hi Gary,

> Generally correct.  
> Thanks for encouragement.

> Tagged\_pointer  
> Thanks for the reference. I hadn’t heard of the term before.

Best wishes,  
Richard

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 9:25pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/6 "2009-12-21T21:25:30Z")

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On Dec 21, 12:26 pm, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > 1. Object\_id’s of Bignum’s close to the boundaries of Fixnum’s bear no  
> > value, left shift it with “1” padding, and make that current  
> > instance variable like “@a”) has an object id. Object id is a  
> > treatment for assignments necessary. Rather, it makes special
> 
> robert
> 
> –  
> remember.guy do |as, often| as.you\_can - without endhttp://blog.rubybestpractices.com/

Hi Robert,

> No variable … has an object id.

Robert, I know, by virtue of reading a number of your responses in  
this NG, that you’re a Ruby expert. But the statement referenced  
above is contradicted by at least two authorities on Ruby:

1. “… every object has a unique object identifier (abbreviated as  
object ID)” [“Programming Ruby”, Second Edition, Thomas, et al, p.  
12] , where you praised the book’s usefulness :-). Of course, the  
“id” method has since be deprecated to “object\_id” when we want to  
reference an object ID.
2. “… an object in Ruby has an identity: “abc”object\_id  
#53744407  
This object ID is of limited utility." [“The Ruby Way”, Second  
Edition, Fulton, p.26]

> step 3 actually mixes two separate things: evaluation of the expression of the right side of “=” and assignment

Granted, I stuck to what I viewed as the essential issues. Perhaps a  
more complete estimate might read.

3.1 Ruby interprets “a = 1” to mean “a.=(1)”, i.e. invokes the “=”  
method on the object. Normally, that reference will cascade up to  
Object.=, I suppose.  
3.1a If “a” is undefined in the current scope, “a” will be added to  
the scope with an ID of (2a+1) = 3.  
3.1b Otherwise:  
3.1.b.1 If a’s ID is in the range of Fixnums, (or a’s ID indicates  
it’s true, false, etc .), a’s ID will be set to 3  
3.1b.2 Otherwise, if a’s ID indicates any other type, a’s ID will be  
pushed to the garbage stack and a’s ID will be set to 3  
Is that better?

> For optimization purposes some object references are special in that they actually _are_ the object

That sounds like you mean in the case of Fixnum “1”, that the number  
1 IS the ID as well as the value of the object. But we can see “puts  
1.object\_id” =\> 3  
So I think that fact (plus all the other evidence I offered) suggests  
that ID’s for Fixnum’s are manufactured as 2\*value+1  
QED???

As always, thanks for your insightful response.  
Richard

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 9:55pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/7 "2009-12-21T21:55:25Z")

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RichardOnRails wrote:

> On Dec 21, 12:26�pm, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > > 1. Object\_id’s of Bignum’s close to the boundaries of Fixnum’s bear no  
> > > value, �left shift it with “1” padding, and make that current  
> > > instance variable like “@a”) has an object id. �Object id is a  
> > > treatment for assignments necessary. �Rather, it makes special
> > 
> > robert
> > 
> > –  
> > remember.guy do |as, often| as.you\_can - without endhttp://blog.rubybestpractices.com/
> 
> Hi Robert,
> 
> > No variable … has an object id.
> 
> Robert, I know, by virtue of reading a number of your responses in  
> this NG, that you�re a Ruby expert. But the statement referenced  
> above is contradicted by at least two authorities on Ruby:
> 
> 1. �… every object has a unique object identifier

Right. The _object_ has an object\_id. The _variable_ that contains it  
does not. The difference is subtle but important.

a = @foo  
b = @foo

a and b hold references to the same object, but they are not the same  
variable. If you do  
a = @bar  
then b is unaffected.

## Best,

Marnen Laibow-Koser

> **[marnen.org: Homepage of Marnen Laibow-Koser](https://marnen.org/)**

[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 21, 2009, 11:15pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/8 "2009-12-21T23:15:33Z")

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On Dec 21, 3:55 pm, Marnen Laibow-Koser [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > > remember.guy do |as, often| as.you\_can - without endhttp://blog.rubybestpractices.com/  
> > > Right. The _object_ has an object\_id. The _variable_ that contains it  
> > > Best,  
> > > –  
> > > Marnen Laibow-Koserhttp://www.marnen.org  
> > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> > > –  
> > > Posted viahttp://www.ruby-forum.com/.

Hi Marnen,

Thanks for that confirmation.

Best wishes,  
Richard

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 22, 2009, 6:48am UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/9 "2009-12-22T06:48:44Z")

</div>

RichardOnRails wrote:

> On Dec 21, 3:55�pm, Marnen Laibow-Koser [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > > > remember.guy do |as, often| as.you\_can - without endhttp://blog.rubybestpractices.com/  
> > > > Right. �The _object_ has an object\_id. �The _variable_ that contains it  
> > > > Best,  
> > > > –  
> > > > Marnen Laibow-Koserhttp://www.marnen.org  
> > > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
> > > > –  
> > > > Posted viahttp://www.ruby-forum.com/.
> 
> Hi Marnen,
> 
> Thanks for that confirmation.

Just to make it perfectly clear: I’m confirming that Robert is right,  
and that there’s no contradiction with the other articles you found. I  
am not confirming what I take to be your hypothesis.

> Best wishes,  
> Richard

## Best,

Marnen Laibow-Koser

> **[marnen.org: Homepage of Marnen Laibow-Koser](https://marnen.org/)**

[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

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**Post date:** [December 22, 2009, 9:28am UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/10 "2009-12-22T09:28:23Z")

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2009/12/21 RichardOnRails  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> On Dec 21, 12:26 pm, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > 2009/12/21 RichardOnRails [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> 1. “… an object in Ruby has an identity: “abc”object\_id  
> #53744407  
> This object ID is of limited utility." [“The Ruby Way”, Second  
> Edition, Fulton, p.26]

As Marnen pointed out already, there is no contradiction between what  
I said and what the authorities said. A variable is just a place to  
store an object reference. Other than that it does not have  
properties, definitively no id. What is returned by invocation of  
#object\_id is attached to the object at hand and not to the variable.  
Whether the object is an immediate value such as a Fixnum or a  
“regular” object (such as String) does not really matter with regard  
to the variable.

> > step 3 actually mixes two separate things: evaluation of the expression of the right side of “=” and assignment
> 
> Granted, I stuck to what I viewed as the essential issues. Perhaps a  
> more complete estimate might read.
> 
> 3.1 Ruby interprets “a = 1” to mean “a.=(1)”, i.e. invokes the “=”  
> method on the object. Normally, that reference will cascade up to  
> Object.=, I suppose.

Now that is completely wrong. “a=1” is an assignment meaning, it  
takes whatever object reference the evaluation of the expression on  
the right side yields and puts it into the storage location denoted by  
“a”. There is no method invoked, certainly no method on “a” which -  
as I said - is no object but just a place in storage.

> 3.1a If “a” is undefined in the current scope, “a” will be added to  
> the scope with an ID of (2a+1) = 3.  
> 3.1b Otherwise:  
> 3.1.b.1 If a’s ID is in the range of Fixnums, (or a’s ID indicates  
> it’s true, false, etc .), a’s ID will be set to 3  
> 3.1b.2 Otherwise, if a’s ID indicates any other type, a’s ID will be  
> pushed to the garbage stack and a’s ID will be set to 3  
> Is that better?

I’m sorry, no. It’s rather:

1. Make sure local scope has a place for variable “a”.
2. Evaluate the expression to the right side of “=”.
3. Take the resulting object reference of step 2 and store it in the  
location for variable “a”.

Steps 1 and 2 can actually be exchanged, it does not really matter much.

> > For optimization purposes some object references are special in that they actually _are_ the object
> 
> That sounds like you mean in the case of Fixnum “1”, that the number  
> 1 IS the ID as well as the value of the object. But we can see “puts  
> 1.object\_id” =\> 3

No, it means that in the case of Fixnum the _reference_ is the object.  
See the article Gary referenced for further detail:

> **[Tagged pointer](https://en.wikipedia.org/wiki/Tagged_pointer)**
>
> In computer science, a tagged pointer is a pointer (concretely a memory address) with additional data associated with it, such as an indirection bit or reference count. This additional data is often "folded" into the pointer, meaning stored inline in the data representing the address, taking advantage of certain properties of memory addressing. The name comes from "tagged architecture" systems, which reserved bits at the hardware level to indicate the significance of each word; the additional dat...

> So I think that fact (plus all the other evidence I offered) suggests  
> that ID’s for Fixnum’s are manufactured as 2\*value+1  
> QED???

The way object ids come into existence is completely unrelated to the  
process of variable assignment. Since in Ruby any object needs an id  
and Fixnums (plus a few more) are immediate values (which means there  
is just an object _reference_ and no object, which btw also means that  
there is no place to store state and hence Fixnums are immutable) it  
was chosen to derive object ids according to the formula you found  
out.

There is probably also a technical reason for this formula which  
likely has to do with the fact that other objects need ids as well and  
calculation of them should be efficient but I believe it is more  
important to understand the object - object reference dichotomy.

Actually, I believe all this reasoning about Fixnums being immediate  
values is totally overdone. From a Ruby programmer’s perspective it  
is completely irrelevant (if you put performance aside for the  
moment). It is sufficient to know that Ruby has variables which  
contain object references and that evaluation of whatever expression  
yields an object reference. The programming model is as simple as  
that. Immediate values are really just an optimization under the hood  
to speed up math and other common operations. In Ruby land, you have  
no chance to distinguish an immediate value from any other immutable  
object - whatever methods you invoke (and there are quite a few for  
Fixnum) the object simply does not change its state. Granted, there  
are a few things that do not work, for example defining a finalizer  
for a Fixnum but even that raises an ordinary exception.

Kind regards

robert

---

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 22, 2009, 3:40pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/11 "2009-12-22T15:40:39Z")

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2009/12/22 Rick DeNatale [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)

> > No, it means that in the case of Fixnum the _reference_ is the object.
> 
> A very good way to express this I think.

Thank you!

> integer.
> 
> But this doesn’t need to be the case, in an implementation which used  
> a different object model for, say GC, and which interposed an  
> indirection, then boxed objects might have an object id field kept  
> with the indirection, so that the object state could be moved without  
> affecting the object\_id.
> 
> Other Ruby implementations like JRuby, Rubinius, Maglev … might  
> implement such stuff in a way similar to MRI, possible with subtle  
> variations, or some might do it radically differently.

Absolutely. Again, when in Ruby land it does not really matter how a  
particular implementation does it as long as the contract stays  
roughly the same (i.e. #object\_id returns something integerish).

> > Fixnum) the object simply does not change its state. Granted, there  
> > are a few things that do not work, for example defining a finalizer  
> > for a Fixnum but even that raises an ordinary exception.
> 
> Agreed, the only time it’s really important is edge-cases, and when  
> writing extensions.

When writing extensions we’re leaving Ruby land and so, yes, chances  
are that you better know how things work under the hood then. Do you  
have any particular edge cases in Ruby land in mind? Off the top of  
my head I cannot think of any.

Kind regards

robert

---

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**Post date:** [December 22, 2009, 2:19pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/12 "2009-12-22T14:19:16Z")

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On Tue, Dec 22, 2009 at 3:24 AM, Robert K.  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> 2009/12/21 RichardOnRails [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> “a”. There is no method invoked, certainly no method on “a” which -  
> as I said - is no object but just a place in storage.

Absolutely correct!

> > 1 IS the ID as well as the value of the object. But we can see “puts  
> > 1.object\_id” =\> 3
> 
> No, it means that in the case of Fixnum the _reference_ is the object.

A very good way to express this I think.

> out.
> 
> There is probably also a technical reason for this formula which  
> likely has to do with the fact that other objects need ids as well and  
> calculation of them should be efficient but I believe it is more  
> important to understand the object - object reference dichotomy.

These things are artifacts of the implementation of the language. I  
believe that in MRI the object\_id is just the reference value ‘cast’  
to a FixNum (or maybe Integer). So for an immediate object it’s a  
particular bit pattern interpreted as an integer, and for boxed  
objects it’s the address of the object’s state interpreted as an  
integer.

But this doesn’t need to be the case, in an implementation which used  
a different object model for, say GC, and which interposed an  
indirection, then boxed objects might have an object id field kept  
with the indirection, so that the object state could be moved without  
affecting the object\_id.

Other Ruby implementations like JRuby, Rubinius, Maglev … might  
implement such stuff in a way similar to MRI, possible with subtle  
variations, or some might do it radically differently.

> Fixnum) the object simply does not change its state. Granted, there  
> are a few things that do not work, for example defining a finalizer  
> for a Fixnum but even that raises an ordinary exception.

Agreed, the only time it’s really important is edge-cases, and when  
writing extensions.

–  
Rick DeNatale

Blog: [http://talklikeaduck.denhaven2.com/](http://talklikeaduck.denhaven2.com/)  
Twitter: [http://twitter.com/RickDeNatale](http://twitter.com/RickDeNatale)  
WWR: [NameBright - Coming Soon](http://www.workingwithrails.com/person/9021-rick-denatale)  
LinkedIn: [http://www.linkedin.com/in/rickdenatale](http://www.linkedin.com/in/rickdenatale)

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 22, 2009, 5:06pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/13 "2009-12-22T17:06:08Z")

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On Dec 22, 9:40 am, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > > > That sounds like you mean in the case of Fixnum “1”, that the number
> 
> > integer.
> 
> > > contain object references and that evaluation of whatever expression  
> > > writing extensions.  
> > > –  
> > > remember.guy do |as, often| as.you\_can - without endhttp://blog.rubybestpractices.com/

Hi Robert and Rick,

Thanks for honoring me with responses to what you guys must view as  
drivel. And I accept the assertion that Ruby recognizes “a=1” as an  
assignment statement rather than an invoking a apparently mythical “=”  
operator.

> > Actually, I believe all this reasoning about Fixnums being immediate  
> > values is totally overdone. From a Ruby programmer’s perspective it  
> > is completely irrelevant (if you put performance aside for the  
> > moment). [snip]  
> > Agreed.

I see your point. But I’ve got a “burr under my intellectual saddle.”  
Both Robert and Matz responded a few weeks ago on a question I raised  
about implementing a Fixnum ++ operator in Ruby functionally  
equivalent to C’s prefix\_++ operator. I’m not lobbying for such a  
change; I merely suggested that it’s possible. The response was such  
an operator would be functionally equivalent to “turning 1 into 2.”

But I see the following:  
a = 1 # ID = 3  
a = 2 # ID = 5  
b = 1 # ID = 1  
b++ # implemented as b.++() which increments b’s object’s ID by 2  
and checks for edge cases; I don’t see such an implementation as  
disturbing any other object, at least none on my machine’s hardware  
and software state.

> “a=1” is an assignment meaning, it  
> takes whatever object reference the evaluation of the expression on  
> the right side yields and puts it into the storage location denoted by  
> “a”. There is no method invoked, certainly no method on “a” which -  
> as I said - is no object but just a place in storage.

But aside from copying (in this case) 1’s ID, Ruby must first look up  
a’s  
presence in the current scope’s portion of the symbol table and if not  
present, insert it, or otherwise deal with the existing ID for the “a”  
entry: (i) if the ID is an actual address of data in some pool,  
decrement its reference count if positive; or (ii) do nothing for  
Fixnums, true, false and nil).

Looking at at actual IDs used on my 1.8.6.x version of Ruby on my  
Windows XP machine, I see these two cases are easily disambiguated:  
(i) ID is an even number greater than 4, perhaps (to account for  
false, true, nil, which are 0,2, 4. respectively) and (ii) everything  
else.

I wouldn’t even have posted my ++ question if I could follow my way  
through Ruby’s C or C++ implementation. But in about my last decade  
before retirement, I was the debugger/enhancer of several  
organization’s apps, so I know daunting the hunt through C/C++ code  
is, especially an app as big as Ruby. But if you pointed me to Ruby’s  
Finite State Machine (there’s GOT to be one), I’d …

With respect to you both, as well as thanks,  
Richard

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<div class="post-metadata">

**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 22, 2009, 5:47pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/14 "2009-12-22T17:47:41Z")

</div>

2009/12/22 RichardOnRails  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> On Dec 22, 9:40 am, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > 2009/12/22 Rick DeNatale [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)
> > 
> > > On Tue, Dec 22, 2009 at 3:24 AM, Robert K.  
> > > [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> > > 
> > > > 2009/12/21 RichardOnRails [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> Thanks for honoring me with responses to what you guys must view as  
> drivel. And I accept the assertion that Ruby recognizes “a=1” as an  
> assignment statement rather than an invoking a apparently mythical “=”  
> operator.

On syntax level it’s an operator as many others but underneath it is  
quite different. If you think about it for a moment this is the only  
operation which can change an object’s state for all non built in  
classes.

> > > Actually, I believe all this reasoning about Fixnums being immediate  
> > > values is totally overdone. From a Ruby programmer’s perspective it  
> > > is completely irrelevant (if you put performance aside for the  
> > > moment). [snip]  
> > > Agreed.
> 
> I see your point. But I’ve got a “burr under my intellectual saddle.”

That must hurt…

> b++ # implemented as b.++() which increments b’s object’s ID by 2  
> and checks for edge cases;

Please forget your idea of object ids being modified. An object id is  
just a derived bit of data. And, btw, object ids _never_ change  
because the identity of an object does not change.

> I don’t see such an implementation as  
> disturbing any other object, at least none on my machine’s hardware  
> and software state.

You are probably overlooking effects on consistency of the whole  
language. While it would be technically doable to introduce ++ into  
the language the consequences are undesirable.

1. prefix ++ operator would change the state of an instance if you  
wanted to roughly retain C++ semantics.

2. This means, that for other (non Fixnum) classes this will happen:

a = anything\_but\_Fixnum()  
b = a  
++a  
b == a # =\> true  
b.equal? a # =\> true, identity does not change

But, if what you wrote were followed (no other object is affected):

a = any\_Fixnum()  
b = a  
++a  
b == a # =\> false  
b.equal? a # =\> false, identity has changed

1. Also, if Fixnums should behave like other classes, suddenly a  
Fixnum becomes mutable, which cannot be since Fixnums are immediate  
and do not have a place to store state that can change.

2. The only salvation is to make “++a” syntactic sugar for “a += 1” or  
rather “a = a + 1” (or maybe even “a = a.succ”), i.e. an expression  
which contains an assignment. Then “b == a” under 2. above would  
return “false” as well and everything is consistent again (assuming  
standard implementations of + which do not change the instance but  
return a new one).

I believe Matz decided against because a) there is a pretty short  
idiom which does this already (“a += 1”) and b) that existing idiom  
has an equals sign in there thus making the assignment obvious; “++a”  
on the contrary does not have an equals sign anywhere and thus would  
obscure the fact that under the hood an assignment is taking place.  
This would make the code harder to read while not bringing any  
benefits to the language.

> > “a=1” is an assignment meaning, it  
> > takes whatever object reference the evaluation of the expression on  
> > the right side yields and puts it into the storage location denoted by  
> > “a”. There is no method invoked, certainly no method on “a” which -  
> > as I said - is no object but just a place in storage.
> 
> But aside from copying (in this case) 1’s ID, Ruby must first look up

Not “1’s ID” is copied but the “reference to 1”. “1” is only special  
in that the reference does not point to an actual object.

> a’s  
> presence in the current scope’s portion of the symbol table and if not  
> present, insert it, or otherwise deal with the existing ID for the “a”  
> entry: (i) if the ID is an actual address of data in some pool,  
> decrement its reference count if positive; or (ii) do nothing for  
> Fixnums, true, false and nil).

AFAIK Ruby has a mark and sweep garbage collector which does not  
employ reference counting.

> **[Garbage collection (computer science)](https://en.wikipedia.org/wiki/Garbage_collection_%28computer_science%29)**
>
> In computer science, garbage collection (GC) is a form of automatic memory management. The garbage collector attempts to reclaim memory that was allocated by the program, but is no longer referenced; such memory is called garbage. Garbage collection was invented by American computer scientist John McCarthy around 1959 to simplify manual memory management in Lisp. Garbage collection relieves the programmer from doing manual memory management, where the programmer specifies what objects to de-allo...

> I wouldn’t even have posted my ++ question if I could follow my way  
> through Ruby’s C or C++ implementation. But in about my last decade  
> before retirement, I was the debugger/enhancer of several  
> organization’s apps, so I know daunting the hunt through C/C++ code  
> is, especially an app as big as Ruby. But if you pointed me to Ruby’s  
> Finite State Machine (there’s GOT to be one), I’d …

I find that hard as well…

Cheers

robert

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<div class="post-metadata">

**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 25, 2009, 3:16pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/15 "2009-12-25T15:16:49Z")

</div>

2009/12/22 Benoit D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> I would add than using i += 1 is often doing it the wrong way in Ruby. We  
> use Enumerable most of the time, and try to not create any index (because  
> that’s awful, you need an initialization(i=0), a step to go forward(i+=1),  
> and you keep a useless index at the end).

Note sure about your “often” - iterating in the majority of cases can  
certainly be done without indexing an Array. There are other uses for  
“a += 1” though - such as counting.

Kind regards

robert

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<div class="post-metadata">

**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 22, 2009, 6:11pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/16 "2009-12-22T18:11:06Z")

</div>

I believe Matz decided against because a) there is a pretty short  
idiom which does this already (“a += 1”) and b) that existing idiom  
has an equals sign in there thus making the assignment obvious; “++a”  
on the contrary does not have an equals sign anywhere and thus would  
obscure the fact that under the hood an assignment is taking place.  
This would make the code harder to read while not bringing any  
benefits to the language.

I would add than using i += 1 is often doing it the wrong way in Ruby.  
We  
use Enumerable most of the time, and try to not create any index  
(because  
that’s awful, you need an initialization(i=0), a step to go  
forward(i+=1),  
and you keep a useless index at the end).

If you really need an index, you can always use #upto , #downto or  
#step.

Every time you need an index (that means the index of the Enumerable  
thing  
you’re iterating is meaningful), you should use #each\_with\_index or  
#with\_index.

For example, This is my last contribution to RPCFN 4 (pretty-printing  
Polynomials):  
[http://github.com/eregon/RPCFN4/blob/master/solutions/benoit\_daloze.rb](http://github.com/eregon/RPCFN4/blob/master/solutions/benoit_daloze.rb)  
Look at the usage of #each\_with\_index, followed by inject.

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<div class="post-metadata">

**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 25, 2009, 5:47pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/17 "2009-12-25T17:47:48Z")

</div>

On 12/23/2009 08:24 PM, RichardOnRails wrote:

> On Dec 22, 11:46 am, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:
> 
> > 2009/12/22 RichardOnRails [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid):

> > > I see your point. But I’ve got a “burr under my intellectual saddle.”  
> > > That must hurt…
> 
> Nah 🙂 It’s just that sometimes, to use a different metaphor, I’m a  
> dog gnawing at a technology bone. But I’ve got to suspend this issue  
> for about 10 days while I concentrate on my brother’s family (coming  
> in from Europe) and my son’s (coming in from the deep South).

I’ll be staying in Europe and keep watching out - your brother can  
safely travel. 🙂

> But, as a Schwarzenegger character once promised, I’ll be back :-).

I feel seriously threatened. 🙂

> Best wishes for the holidays,

To you, your family and all other members of the Ruby community, too.

Happy Christmas

robert

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**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 25, 2009, 5:00pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/18 "2009-12-25T17:00:10Z")

</div>

On Dec 22, 11:46 am, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > assignment statement rather than an invoking a apparently mythical “=”
> > 
> > > > moment). [snip]  
> > > > an operator would be functionally equivalent to “turning 1 into 2.”  
> > > > because the identity of an object does not change.  
> > > > wanted to roughly retain C++ semantics.
> 
> 1. The only salvation is to make “++a” syntactic sugar for “a += 1” or  
> obscure the fact that under the hood an assignment is taking place.
> 
> AFAIK Ruby has a mark and sweep garbage collector which does not
> 
> Cheers
> 
> robert
> 
> –  
> remember.guy do |as, often| as.you\_can - without endhttp://blog.rubybestpractices.com/

Thanks for your additional response.

> > I see your point. But I’ve got a “burr under my intellectual saddle.”
> 
> That must hurt…

Nah 🙂 It’s just that sometimes, to use a different metaphor, I’m a  
dog gnawing at a technology bone. But I’ve got to suspend this issue  
for about 10 days while I concentrate on my brother’s family (coming  
in from Europe) and my son’s (coming in from the deep South).

But, as a Schwarzenegger character once promised, I’ll be back :-).

Best wishes for the holidays,  
Richard

---

<div class="post-metadata">

**Author:** ![RichardOnRails](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e0b2c6/32.png) [@RichardOnRails](https://www.ruby-forum.com/u/RichardOnRails)\
**Post date:** [December 25, 2009, 7:55pm UTC](https://www.ruby-forum.com/t/rubys-implementation-of-fixnum-assignment/180549/19 "2009-12-25T19:55:31Z")

</div>

On Dec 24, 6:32 am, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> > in from Europe) and my son’s (coming in from the deep South).  
> > To you, your family and all other members of the Ruby community, too.
> 
> Happy Christmas
> 
> ```
> robert
> 
> ```
> 
> –  
> remember.guy do |as, often| as.you\_can - without endhttp://blog.rubybestpractices.com/

> I’ll be staying in Europe and keep watching out - your brother can  
> safely travel. 🙂

It’s good to have friends “across the pond”.

> Happy Christmas

Likewise to you, Robert. I like the way I recall Tiny Tim or his  
father said it: Happy Christmas to all,

Richard