# Interesting behaviour

**URL:** <https://www.ruby-forum.com/t/interesting-behaviour/173021>\
**Category:** Ruby\
**Created:** [July 31, 2009, 1:33pm UTC](https://www.ruby-forum.com/t/interesting-behaviour/173021 "2009-07-31T13:33:52Z")\
**Posts on this page:** 4\
**Page:** 1

<div class="post-metadata">

**Author:** ![Deepak\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/22d042/32.png) [@Deepak\_G](https://www.ruby-forum.com/u/Deepak_G)\
**Post date:** [July 31, 2009, 1:33pm UTC](https://www.ruby-forum.com/t/interesting-behaviour/173021/1 "2009-07-31T13:33:52Z")

</div>

When I does following thing on irb console

def foo  
1  
end

foo ===\>o/p 1  
foo.foo ===\>o/p 1  
foo.foo.foo ===\>o/p 1  
foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo…foo  
===\>o/p 1

I got above o/p

* * *

But when I done same thing in Scite editor. I got error

def foo  
1  
end

p foo  
p foo.foo =\>o/p private method `foo’ called for 1:Fixnum  
(NoMethodError)

How ??

thanks  
DG

---

<div class="post-metadata">

**Author:** ![Deepak\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/22d042/32.png) [@Deepak\_G](https://www.ruby-forum.com/u/Deepak_G)\
**Post date:** [July 31, 2009, 2:21pm UTC](https://www.ruby-forum.com/t/interesting-behaviour/173021/2 "2009-07-31T14:21:50Z")

</div>

Deepak G. wrote:

> def foo  
> 1  
> end
> 
> foo ===\>o/p 1  
> foo.foo ===\>o/p 1  
> foo.foo.foo ===\>o/p 1  
> foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo.foo…foo  
> ===\>o/p 1
> 
> I got above o/p

I see the same with ruby 1.8.6.

It looks like you have defined foo as a method in Object, and hence is  
available to all objects:

> > def foo; 1; end  
> > =\> nil
> 
> > “hello”.foo  
> > =\> 1
> 
> > Object.instance\_methods.grep(/foo/)  
> > =\> [“foo”]

Ruby 1.9 makes this slightly better by making the method private:

$ irb19 --simple-prompt

> > “hello”.foo  
> > NoMethodError: undefined method `foo' for "hello":String from (irb):1 from /usr/local/bin/irb19:12:in`’
> 
> > def foo; 1; end  
> > =\> nil
> 
> > “hello”.foo  
> > NoMethodError: private method `foo' called for "hello":String from (irb):3 from /usr/local/bin/irb19:12:in`’
> 
> > Object.private\_instance\_methods.grep(/foo/)  
> > =\> [:foo]

I’m not sure why irb doesn’t define methods as singleton methods of the  
‘main’ (top level) object. You can do this yourself with a bit of  
fiddling:

> > class \<\< self; self; end.class\_eval { def bar; 2; end }  
> > =\> nil
> 
> > bar  
> > =\> 2
> 
> > 1.bar  
> > NoMethodError: undefined method `bar' for 1:Fixnum from (irb):4 from /usr/local/bin/irb19:12:in`’

---

<div class="post-metadata">

**Author:** ![Deepak\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/22d042/32.png) [@Deepak\_G](https://www.ruby-forum.com/u/Deepak_G)\
**Post date:** [July 31, 2009, 2:25pm UTC](https://www.ruby-forum.com/t/interesting-behaviour/173021/3 "2009-07-31T14:25:57Z")

</div>

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

> foo.foo.foo ===\>o/p 1  
> def foo  
> 1  
> end
> 
> p foo  
> p foo.foo =\>o/p private method `foo’ called for 1:Fixnum (NoMethodError)
> 
> How ??

Why? Ask youself why foo.foo.foo → 1 in the irb console!

Try: self.class  
in both Scite and irb…

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<div class="post-metadata">

**Author:** ![Deepak\_G](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/22d042/32.png) [@Deepak\_G](https://www.ruby-forum.com/u/Deepak_G)\
**Post date:** [July 31, 2009, 2:59pm UTC](https://www.ruby-forum.com/t/interesting-behaviour/173021/4 "2009-07-31T14:59:02Z")

</div>

Pascal J. Bourguignon wrote:

> Why? Ask youself why foo.foo.foo --\> 1 in the irb console!
> 
> Try: self.class  
> in both Scite and irb…

It’s not quite as simple as just looking at ‘self’, and it took me a  
long time to find out why.

Ruby has a concept of a ‘the current object’ which is exposed using  
‘self’, but there is also a more hidden concept of ‘the current class’  
where method definitions go. I don’t think there’s an easy way to see  
the current class, but you can set it using class or class\_eval.

> > class Foo; end  
> > =\> nil
> 
> > Foo.instance\_eval { p self }  
> > Foo  
> > =\> nil
> 
> > Foo.instance\_eval { def bar; puts “bar”; end }  
> > =\> nil
> 
> > Foo.bar  
> > bar  
> > =\> nil
> 
> > Foo.new.bar  
> > NoMethodError: undefined method `bar’ for #Foo:0xb7c89710  
> > from (irb):5  
> > from :0

But:

> > Foo.class\_eval { p self }  
> > Foo  
> > =\> nil
> 
> > Foo.class\_eval { def baz; puts “baz”; end }  
> > =\> nil
> 
> > Foo.baz  
> > NoMethodError: undefined method `baz’ for Foo:Class  
> > from (irb):8  
> > from :0
> 
> > Foo.new.baz  
> > baz  
> > =\> nil

So in both cases, self is the class Foo, but in the first case methods  
are defined in the singleton class of Foo, whilst in the second case  
they are defined as instance methods in the class Foo.