# A question about Ruby main object

**URL:** <https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535>\
**Category:** Ruby\
**Created:** [January 2, 2006, 7:24pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535 "2006-01-02T19:24:49Z")\
**Posts on this page:** 11\
**Page:** 1

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**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 2, 2006, 7:24pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/1 "2006-01-02T19:24:49Z")

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Hi!

I have been doing different things w/ Ruby for a couple of years now  
and  
the only bad thing I can say about it is that it makes programming in  
other  
languages feel awfully burdensome. = )

Anyhow, I really like how everything makes sense. There is one thing  
that  
I have not been able to fit in entirely. A Ruby program starts in the  
context of the “main” object,

antti@hyperion:~\> ruby -e “puts self”  
main  
antti@hyperion:~\> ruby -e “puts self.class”  
Object

However, the methods I declare in the context of this “main” object  
are  
somehow available as private methods of class Object (and naturally  
usable  
from subclasses):

def foo  
puts “hello”  
end  
class Bar  
def amethod  
foo  
end  
end  
b = Bar.new  
b.amethod

outputs:  
hello

Is there some logical explanation for this? I understand that this is  
very  
convenient as these methods appear as “stand-alone functions”, but  
taking  
it just as “it just is so” breaks the otherwise consistent rules, as  
normally you have to define a method in the context of a class for it to  
be  
a method of that class. However, the “main” object is not class Object,  
nor  
is it a class at all:

antti@hyperion:~\> ruby -e “puts self.kind\_of?(Class)”  
false  
antti@hyperion:~\> ruby -e “puts self.kind\_of?(Module)”  
false

So what is the logic behind the “main” object? Is there a logical  
reason  
for the methods defined in its context to appear as private methods of  
class Object?

```
    -Antti-
```

---

<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 2, 2006, 8:06pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/2 "2006-01-02T20:06:15Z")

</div>

See

[http://groups.google.com/group/comp.lang.ruby/browse\_thread/thread/7bb7b451a8f3cca7/98c4c62127b9d945?q=itsme213+main+singleton+Object&rnum=1#98c4c62127b9d945](http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/7bb7b451a8f3cca7/98c4c62127b9d945?q=itsme213+main+singleton+Object&rnum=1#98c4c62127b9d945)

“Antti Karanta” [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote in  
message  
news:dpbr1c$p2b$removed\_email\_address@domain.invalid…

---

<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 2, 2006, 8:27pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/3 "2006-01-02T20:27:29Z")

</div>

Antti Karanta wrote:

> Is there some logical explanation for this? I understand that this is very  
> convenient as these methods appear as “stand-alone functions”, but taking  
> it just as “it just is so” breaks the otherwise consistent rules, as  
> normally you have to define a method in the context of a class for it to be  
> a method of that class. However, the “main” object is not class Object, nor  
> is it a class at all:

Note that you are not doing def self.method() end. It’s just that def  
method() end at the top level adds the methods to the Kernel module  
(which is included in Object meaning its methods are available  
everywhere) instead of raising an exception or adding them to the top  
level object itself.

It’s also interesting to see which singleton methods the top level  
object has:

> ruby -e “p methods(false)”  
> [“include”, “private”, “to\_s”, “public”]

to\_s is so you see “main” when doing p self etc. at the top level.  
The other three ones are top level versions of the respective instance  
method of Module.

---

<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 2, 2006, 8:48pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/4 "2006-01-02T20:48:38Z")

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Antti Karanta wrote:

> So what is the logic behind the “main” object? Is there a logical reason  
> for the methods defined in its context to appear as private methods of  
> class Object?

To quote Guy Decoux:

> when you define a method in A, this will be an instance method for A

Now, I have a question for Guy:

Flagellate = Class.new {  
def banana\_boat; puts ‘hurrah!’ end  
}

makes banana\_boat a method on Flagellate, which makes me think that  
methods go where self is.

However:

class FranklinRoosevelt  
def smooth\_operator; def banana\_boat; puts ‘javohl!’ end end  
end  
FranklinRoosevelt.new.smooth\_operator

makes banana\_boat a method on FranklinRoosevelt, which is either  
ruby\_class or self.class, but not self.

What’s goin’ on? Is there another internal variable that determines  
where methods go, or am I confusing things? Are Class.new and class\_eval  
just the exception to the rule that method definitions go on ruby\_class?  
If so, how?

Devin

---

<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 3, 2006, 12:19pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/5 "2006-01-03T12:19:38Z")

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> > > > > “t” == ts [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

t\> many persons will except that ruby will do the same that if you  
write  
^^^^^^  
expect

l’anglais est vraiment tres etrange 🙂

Guy Decoux

---

<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 3, 2006, 11:10am UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/6 "2006-01-03T11:10:05Z")

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> > > > > “D” == Devin M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

D\> Flagellate = Class.new {  
D\> def banana\_boat; puts ‘hurrah!’ end  
D\> }

With this you have this case

> > - in the class A, it has : self = A, ruby\_class = A

This mean that you have self = ruby\_class = Flagellate

D\> However:

D\> class FranklinRoosevelt  
D\> def smooth\_operator; def banana\_boat; puts ‘javohl!’ end end  
D\> end  
D\> FranklinRoosevelt.new.smooth\_operator

D\> makes banana\_boat a method on FranklinRoosevelt, which is either  
D\> ruby\_class or self.class, but not self.

When the method #smoot\_operator is called

- self is an instance of FranklinRoosevelt
- ruby\_class is FranklinRoosevelt

#banana\_boot become a method on FranklinRoosevelt

D\> What’s goin’ on? Is there another internal variable that determines  
D\> where methods go, or am I confusing things?

You are confusing : the problem is that you can’t access the variable  
ruby\_class, it’s completely hidden but ruby always use this variable to  
know where it must store a method.

D\> Are Class.new and class\_eval just the exception to the rule that  
method  
D\> definitions go on ruby\_class? If so, how?

No, they are not exceptions. This is just that when you write

Flagellate = Class.new {  
def banana\_boat; puts ‘hurrah!’ end  
}

many persons will except that ruby will do the same that if you write

class Flagellate  
def banana\_boat; puts ‘hurrah!’ end  
end

This is why it define self = ruby\_class = Flagellate

Guy Decoux

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<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 3, 2006, 1:17pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/7 "2006-01-03T13:17:23Z")

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> > > > > “D” == Devin M. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) writes:

D\> Thanks. It turns out my confusion is with constants and  
class-variables  
D\> (whose destination I’d figured was based on ruby\_class), not methods,  
D\> since:

Perhaps best to don’t speak about class-variable because it seems to be  
a  
_true_ POLS, i.e. only matz is not surprised 🙂

D\> Loves me some complex grammar rules…

It don’t exist complex grammar rules, ruby just try to follow matz’s  
POLS

Guy Decoux

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<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 3, 2006, 1:04pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/8 "2006-01-03T13:04:56Z")

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ts wrote:

> t\> many persons will except that ruby will do the same that if you write  
> ^^^^^^  
> expect
> 
> l’anglais est vraiment tres etrange 🙂

Nah… 'snot that bad… 🙂

Thanks. It turns out my confusion is with constants and class-variables  
(whose destination I’d figured was based on ruby\_class), not methods,  
since:

irb(main):001:0\> Foo = Class.new {  
irb(main):002:1\* FOO = 5  
irb(main):003:1\> }  
=\> Foo  
irb(main):004:0\> FOO  
=\> 5  
irb(main):005:0\> Foo.class\_eval {  
irb(main):006:1\* @@foo = 5  
irb(main):007:1\> }  
=\> 5  
irb(main):008:0\> @@foo  
=\> 5

What determines where _they_ go?

Thanks,  
Devin  
Loves me some complex grammar rules…

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<div class="post-metadata">

**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 3, 2006, 4:13pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/9 "2006-01-03T16:13:14Z")

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

> D\> Loves me some complex grammar rules…
> 
> It don’t exist complex grammar rules, ruby just try to follow  
> matz’s POLS

I can assure you that the Ruby grammar has pretty complex rules if  
you’re interested in parsing it.

-mental

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**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 4, 2006, 6:09pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/10 "2006-01-04T18:09:54Z")

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ts wrote:

> D\> Loves me some complex grammar rules…
> 
> It don’t exist complex grammar rules, ruby just try to follow matz’s POLS

I was talking about English… 😛

---

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**Author:** ![Antti\_Karanta](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/aeb1de/32.png) [@Antti\_Karanta](https://www.ruby-forum.com/u/Antti_Karanta)\
**Post date:** [January 3, 2006, 8:30pm UTC](https://www.ruby-forum.com/t/a-question-about-ruby-main-object/51535/11 "2006-01-03T20:30:25Z")

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itsme213 wrote:

> See
> 
> [http://groups.google.com/group/comp.lang.ruby/browse\_thread/thread/7bb7b451a8f3cca7/98c4c62127b9d945?q=itsme213+main+singleton+Object&rnum=1#98c4c62127b9d945](http://groups.google.com/group/comp.lang.ruby/browse_thread/thread/7bb7b451a8f3cca7/98c4c62127b9d945?q=itsme213+main+singleton+Object&rnum=1#98c4c62127b9d945)

Thanks, this cleared it up. Weird I did not bump into that thread w/  
google…

```
   -Antti-

```