# Access modifier : private

**URL:** <https://www.ruby-forum.com/t/access-modifier-private/121135>\
**Category:** Ruby\
**Created:** [November 24, 2007, 10:57am UTC](https://www.ruby-forum.com/t/access-modifier-private/121135 "2007-11-24T10:57:19Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![dharmarth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3e96dc/32.png) [@dharmarth](https://www.ruby-forum.com/u/dharmarth)\
**Post date:** [November 24, 2007, 10:57am UTC](https://www.ruby-forum.com/t/access-modifier-private/121135/1 "2007-11-24T10:57:19Z")

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Hi!

I’m missing some core ruby concept here that I just can’t figure out;  
any assistance would be excellent and welcome:

I came to know from various posts that Class level varibales are  
shared among its subclasses in 1.8.

But my confusion is, even though i mark it as private, it is  
accessible in subclass. See example below for more clarity on doubt.

class Test1  
private  
@@v=10  
end

class Test2 \< Test1  
def pr  
@@v=12  
puts @@v  
end  
end

Test2.new.pr

## ~Dharmarth

“When I let go of what I am, I become what I might be.”

---

<div class="post-metadata">

**Author:** ![dharmarth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3e96dc/32.png) [@dharmarth](https://www.ruby-forum.com/u/dharmarth)\
**Post date:** [November 24, 2007, 11:25am UTC](https://www.ruby-forum.com/t/access-modifier-private/121135/2 "2007-11-24T11:25:29Z")

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Alle sabato 24 novembre 2007, Dharmarth S. ha scritto:

> end
> 
> Test2.new.pr
> 
> ## ~Dharmarth
> 
> “When I let go of what I am, I become what I might be.”

First of all, private only works for instance methods, not for  
variables,  
either instance variables or class variables, which are always private.  
Second, the meaning of “private” in ruby is different from what you have  
in  
other languages such as C++. In ruby, “private” only means you can’t  
call it  
with a receiver (i.e, using the form receiver.method). This means that a  
method declared private in a class can be called in a subclass. The same  
is  
true for instance variables (writing rec.@var gives a syntax error,  
which is  
the reason instance variables are always private). Here are some  
examples:

class A  
def initialize  
@x=1  
end

def m1  
puts “m1 calling m”  
m  
end

def m2  
puts “m2 calling self.m”  
self.m  
end

def m3 other  
puts “m3 calling m on other instance of class A”  
other.m  
end

private  
def m  
puts “m”  
end

end

class B \< A

def mb1  
puts “@x is: #{@x}”  
end

def mb2  
puts “mb2 calling m”  
m  
end

end

After loading the previous code in IRB (from the file test\_private.rb),  
I run  
the methods defined for A and B, with the following results:  
irb(main):001:0\> require ‘test\_private’  
=\> true  
irb(main):002:0\> a = A.new  
=\> #\<A:0xb78da7b8 @x=1\>  
irb(main):003:0\> a.m1  
m1 calling m  
m  
=\> nil  
irb(main):004:0\> a.m2  
m2 calling self.m  
NoMethodError: private method `m' called for #<A:0xb78da7b8 @x=1> from ./prova.rb:14:in`m2’  
from (irb):4  
irb(main):005:0\> a.m3 A.new  
m3 calling m on other instance of class A  
NoMethodError: private method `m' called for #<A:0xb78d44f8 @x=1> from ./prova.rb:19:in`m3’  
from (irb):6  
irb(main):006:0\> b = B.new  
=\> #\<B:0xb78d257c @x=1\>  
irb(main):007:0\> b.mb1  
@x is: 1  
=\> nil  
irb(main):008:0\> b.mb2  
mb2 calling m  
m  
=\> nil

A#m1, obviously, works. A#m2 doesn’t work because it calls m using a  
receiver,  
which is forbidden (even when the receiver is the implicit receiver,  
self).  
A#m3 doesn’t work because it calls m with a receiver (even if of the  
same  
class as self). B#bm1 works, because the instance variable is called  
without  
a receiver. B#mb2 works, because it’s calling the method without the  
receiver. The fact that the method is private doesn’t matter.

I hope this helps

Stefano

---

<div class="post-metadata">

**Author:** ![dharmarth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3e96dc/32.png) [@dharmarth](https://www.ruby-forum.com/u/dharmarth)\
**Post date:** [November 24, 2007, 12:57pm UTC](https://www.ruby-forum.com/t/access-modifier-private/121135/3 "2007-11-24T12:57:43Z")

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Thanks a lot Stefano! That was really helpful.

One more help.

What’s the rationale in sharing Class level variables with subclasses?  
Is there any way to restrict Class level variables and Class level  
methods to restrict to class itself?

~Dharmarth

---

<div class="post-metadata">

**Author:** ![dharmarth](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/d/3e96dc/32.png) [@dharmarth](https://www.ruby-forum.com/u/dharmarth)\
**Post date:** [November 24, 2007, 3:40pm UTC](https://www.ruby-forum.com/t/access-modifier-private/121135/4 "2007-11-24T15:40:31Z")

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On Nov 24, 4:57 am, Dharmarth S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> Thanks a lot Stefano! That was really helpful.
> 
> One more help.
> 
> What’s the rationale in sharing Class level variables with subclasses?  
> Is there any way to restrict Class level variables and Class level  
> methods to restrict to class itself?

Instead of using class level variables, use instance variables of the  
class itself. It’s what most people want anyhow:

irb(main):001:0\> class Foo  
irb(main):002:1\> @jim = :foo  
irb(main):003:1\> class \<\< self  
irb(main):004:2\> attr\_accessor :jim  
irb(main):005:2\> end  
irb(main):006:1\> end

irb(main):007:0\> class Bar \< Foo  
irb(main):008:1\> @jim = :bar  
irb(main):011:1\> end

irb(main):012:0\> Foo.jim  
=\> :foo

irb(main):013:0\> Bar.jim  
=\> :bar

irb(main):014:0\> Foo.jim = 42  
=\> 42

irb(main):015:0\> Bar.jim  
=\> :bar

irb(main):016:0\> Bar.jim = ‘whee’  
=\> “whee”

irb(main):017:0\> Foo.jim  
=\> 42

etc.