# Re: metaprogramming surprise?

**URL:** <https://www.ruby-forum.com/t/re-metaprogramming-surprise/73064>\
**Category:** Ruby\
**Created:** [October 20, 2006, 11:23pm UTC](https://www.ruby-forum.com/t/re-metaprogramming-surprise/73064 "2006-10-20T23:23:38Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![phrogz](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/2acd7d/32.png) [@phrogz](https://www.ruby-forum.com/u/phrogz)\
**Post date:** [October 20, 2006, 11:23pm UTC](https://www.ruby-forum.com/t/re-metaprogramming-surprise/73064/1 "2006-10-20T23:23:38Z")

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From: Garance A Drosehn [[mailto:removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)]

> > Any chance that class variables will disappear in Ruby 2.0?  
> > I’m only half joking.
> 
> I use them fairly frequently, and have never been tripped up by them.  
> They seem like a pretty straightforward idea to me. I tend to use  
> them  
> for “config-ish” things in the class, which would need to  
> have the same value in all instances of the class.

Do you rely on the fact that subclasses will share the same  
variables/values? Or do you rarely subclass class that you’re using  
class variables on?

Out of curiosity, why do you think that you use them instead of class  
instance variables? Because they’re slightly more convenient to access  
from the instance?

class Foo  
@whee = ‘FOOwhee’  
class \<\< self  
attr\_reader :whee  
end

@@gibble = ‘FOOgibble’  
def self.gibble  
@@gibble  
end

def stuff  
“#{self.class} ##{object\_id} says whee is ‘#{self.class.whee}’” +  
" and gibble is ‘#@@gibble’"  
end  
end

class Bar \< Foo  
@whee = ‘BARwhee’  
@@gibble = ‘BARgibble’  
end

p Foo.whee, Bar.whee  
#=\> “FOOwhee”  
#=\> “BARwhee”

p Foo.gibble, Bar.gibble  
#=\> “BARgibble”  
#=\> “BARgibble”

f1,f2 = Foo.new, Foo.new  
b1,b2 = Bar.new, Bar.new  
p f1.stuff, f2.stuff, b1.stuff, b2.stuff  
#=\> “Foo #21076010 says whee is ‘FOOwhee’ and gibble is ‘BARgibble’”  
#=\> “Foo #21075960 says whee is ‘FOOwhee’ and gibble is ‘BARgibble’”  
#=\> “Bar #21075920 says whee is ‘BARwhee’ and gibble is ‘BARgibble’”  
#=\> “Bar #21075910 says whee is ‘BARwhee’ and gibble is ‘BARgibble’”