# Immutable Ruby

**URL:** <https://www.ruby-forum.com/t/immutable-ruby/147174>\
**Category:** Ruby\
**Created:** [August 29, 2008, 3:24am UTC](https://www.ruby-forum.com/t/immutable-ruby/147174 "2008-08-29T03:24:31Z")\
**Posts on this page:** 9\
**Page:** 1

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 29, 2008, 3:24am UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/1 "2008-08-29T03:24:31Z")

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I was thinking about Erlang a bit today, the fact that it’s objects  
are all immutable and it’s usefulness to concurrency. So I began to  
wonder, what would an Immutable Ruby look like?

- Would it make setter methods effectively pointless?
- Overall, would it help or hurt efficiency/speed?
- Would it ruin Ruby’s elegance?
- No more #\<\< ☹
- No more Symbol vs. String!!! 🙂
- Is such a thing even possible?

T.

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 29, 2008, 6:24am UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/2 "2008-08-29T06:24:04Z")

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Hi,

In message “Re: Immutable Ruby”  
on Fri, 29 Aug 2008 10:19:15 +0900, Trans [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
writes:

|I was thinking about Erlang a bit today, the fact that it’s objects  
|are all immutable and it’s usefulness to concurrency. So I began to  
|wonder, what would an Immutable Ruby look like?

I have once dreamed of a such language, and had a conclusion that was  
not Ruby at least, although a pretty interesting language.

```
          matz.

```

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<div class="post-metadata">

**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 29, 2008, 9:15pm UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/3 "2008-08-29T21:15:10Z")

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On Fri, 29 Aug 2008, Trans wrote:

> I was thinking about Erlang a bit today, the fact that it’s objects  
> are all immutable and it’s usefulness to concurrency. So I began to  
> wonder, what would an Immutable Ruby look like?
> 
> - Would it make setter methods effectively pointless?

The notion of a setter is probably very problematic.

> - Overall, would it help or hurt efficiency/speed?

Depends on a single processor slower, on a high concurrency N core  
processor, faster.

> - Would it ruin Ruby’s elegance?

Yes, no. It becomes conceptually cleaner. The garbage collection becomes  
cleaner and easier.

I suspect it will force you to think to really really think about  
which class owns which other class.

> - No more #\<\< ☹  
> Nor any ! method.

> - Is such a thing even possible?

Sort like Star Trek… “It’s life Jim, but not as we know it”

To find out what it would be like replace every  
Blah.new(arg1,arg2…)  
with  
Blah.new(arg1,arg2…).freeze

John C. Phone : (64)(3) 358 6639  
Tait Electronics Fax : (64)(3) 359 4632  
PO Box 1645 Christchurch Email : removed\_email\_address@domain.invalid  
New Zealand

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 29, 2008, 10:21pm UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/4 "2008-08-29T22:21:58Z")

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Hi –

On Sat, 30 Aug 2008, Trans wrote:

> > |wonder, what would an Immutable Ruby look like?
> > 
> > I have once dreamed of a such language, and had a conclusion that was  
> > not Ruby at least, although a pretty interesting language.
> 
> Does that mean you think Immutable Ruby would be so different a  
> language as to no longer be recognizable as Ruby? Perhaps so. The  
> prospect is very interesting to me nonetheless. If I did not have to  
> worry so much about $$$$, I would very much like to try my hand at  
> writing an Immutable Ruby in Erlang.

I don’t think it would be recognizable as Ruby. Consider this:

$ ./ruby -ve ‘a = Object.new; class \<\< a;  
def talk; print “hi\n”; end;  
end; a.talk’  
ruby - version 1.0-971225 (i686-linux)  
hi

If you change print to puts, it won’t know what you mean. And don’t  
ask a for its .methods either. In other words, per-object differential  
behavior was part of Ruby before puts and methods were. I’d say it’s  
pretty fundamental 🙂

(If anyone wants my hacked copy of Ruby 1.0 (hacked to compile on gcc  
4.0, for some definitions of “compile”), let me know.)

David

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 29, 2008, 10:14pm UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/5 "2008-08-29T22:14:21Z")

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On Aug 29, 12:18 am, Yukihiro M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> not Ruby at least, although a pretty interesting language.  
> Does that mean you think Immutable Ruby would be so different a  
> language as to no longer be recognizable as Ruby? Perhaps so. The  
> prospect is very interesting to me nonetheless. If I did not have to  
> worry so much about $$$$, I would very much like to try my hand at  
> writing an Immutable Ruby in Erlang.

T.

---

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 29, 2008, 10:40pm UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/6 "2008-08-29T22:40:44Z")

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John C. wrote:

> To find out what it would be like replace every  
> Blah.new(arg1,arg2…)  
> with  
> Blah.new(arg1,arg2…).freeze

$".freeze  
require “fileutils”

Life is not good. Beam me up Scotty.

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 30, 2008, 12:06am UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/7 "2008-08-30T00:06:50Z")

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On Aug 28, 10:07 pm, John C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> To find out what it would be like replace every  
> Blah.new(arg1,arg2…)  
> with  
> Blah.new(arg1,arg2…).freeze

Almost. From my understanding Immutable objects can have internal  
changing state as long as it is never exposed to the outside world.  
For instance, memoize is a good example.

Am I right about that?

T.

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 29, 2008, 10:30pm UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/8 "2008-08-29T22:30:45Z")

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

> ```
> If I did not have to
> 
> ```
> 
> worry so much about $$$$, I would very much like to try my hand at  
> writing an Immutable Ruby in Erlang.

Sounds similar to what Tony’s thinking about with Reia.  
[http://wiki.reia-lang.org/wiki/Main\_Page](http://wiki.reia-lang.org/wiki/Main_Page)

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**Author:** ![tcsnide](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/eb8c5e/32.png) [@tcsnide](https://www.ruby-forum.com/u/tcsnide)\
**Post date:** [August 30, 2008, 12:51am UTC](https://www.ruby-forum.com/t/immutable-ruby/147174/9 "2008-08-30T00:51:53Z")

</div>

On Fri, Aug 29, 2008 at 2:21 PM, Steven P. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)  
wrote:

> Sounds similar to what Tony’s thinking about with Reia.  
> [http://wiki.reia-lang.org/wiki/Main\_Page](http://wiki.reia-lang.org/wiki/Main_Page)

Yep, thanks for mentioning it.

> - No more #\<\< ☹

Reia doesn’t support \<\< for syntactic reasons (in Reia this designates  
the beginning of a “binary”) but it will allow “mutation” of its  
pseudo-objects (Lists, Dicts, etc.) using a “magic rebinding”  
technique (not presently implemented). This does differ somewhat from  
Ruby’s semantics. Consider the following in Ruby:

> > a = b = [1,2,3]  
> > =\> [1, 2, 3]  
> > a \<\< 4  
> > =\> [1, 2, 3, 4]  
> > b  
> > =\> [1, 2, 3, 4]

Here a and b reference the same Array, so when you mutate a the  
contents of b also change. However, in Reia (this example actually  
works from its current interactive interpreter):

> > a = b = [1,2,3]  
> > =\> [1,2,3]  
> > a.push(4)  
> > =\> [1,2,3,4]  
> > b  
> > =\> [1,2,3]

Reia allows rebinding by compiling to static single assignment form  
(currently in development). This decomposes places where variables  
are potentially rebound into single assignment by keeping track of  
versions of variables. When you a.push(4) in Reia, it (will  
eventually be able to) create a new version of the a variable which is  
bound to the new version of the list. However, the value of b does  
not change.

Is this confusing? Hard to say. I personally don’t find it  
confusing, but YMMV.

> - No more Symbol vs. String!!! 🙂

Immutable strings are somewhat different from symbols. Erlang has  
both (except it calls symbols “atoms”). Symbols work off of what’s  
effectively a big global hash table. With immutable strings you can  
have several copies which are identical but still require O(n)  
comparisons and so forth.

> Nor any ! method.

I plan on carrying over the method! convention and semantics into  
Reia, FWIW. method? is coming along as well.

That said I find it nice the “default” approach in Ruby is to not  
modify the receiver.