Re: WTF is Struct? Oh! [was Re: Ruby beginner question 2]

On Aug 22, 2005, at 6:47 AM, Alexander Kellett wrote:
> yup. though don't be caught by this:
>
> irb(main):003:0> B=Struct.new :g
> => B
> irb(main):004:0> class B; def blah; p @g; end; end
> => nil
> irb(main):005:0> B.new(5).blah
> nil
> => nil

Yeah, as I was writing up my suggested example for the docs, I  
noticed that the properties weren't available as instance variables,  
and I needed to use the accessor methods instead to read the values.

Indeed, it looks like instances of the Struct somehow magically store  
their internal state in the ether:
irb(main):001:0> Klass = Struct.new( :foo, :bar )
=> Klass
irb(main):002:0> instance = Klass.new( 'f', 'b' )
=> #<struct Klass foo="f", bar="b">
irb(main):003:0> instance.instance_variables
=> []

Is this is a case where some internal details are being magically  
hidden by the C side? Or is it possible in Ruby to have an instance  
variable that doesn't show up in #instance_variables?