Re: JRuby/Ruby top-level classes? (Fwd: Metaclasses)

On Fri, 9 Nov 2007, Giles Bowkett wrote:

> A poster on ruby-talk came across differences in Ruby's and JRuby's
> top-level classes. I e-mailed Charles Nutter to ask if the differences
        [...]
> Here's the relevant stuff from the original post:
> 
> ---------- Forwarded message ----------
> Hi, all.  I'm trying to understand chapter 24 of Programming Ruby.
> I'm using "metaid.rb" from why the lucky stiff's site to help with the
> examples. (http://whytheluckystiff.net/articles/seeingMetaclassesClearly.html)
> 
> Everything is pretty straightforward except for the diagrams of
> inheritance of metaclasses.  Figure 24.2 indicates that for a direct
> subclass of Object, its metaclass's superclass should be Object's
> metaclass.  When I try this out in irb, I don't get the expected
> result.
> 
> $ irb -r metaid
> irb(main):001:0> String.metaclass
> => #<Class:String>
> irb(main):002:0> String.metaclass.superclass
> => #<Class:Class>
> irb(main):003:0> String.metaclass.superclass == Object.metaclass
> => false
> 
> Surprisingly, when I try it in JRuby, I do get the expected result.
> 
> $ jirb -r metaid
> irb(main):001:0> String.metaclass
> => #<Class:String>
> irb(main):002:0> String.metaclass.superclass
> => #<Class:Object>
> irb(main):003:0> String.metaclass.superclass == Object.metaclass
> => true
> 
> Also, figure 24.3 suggests that for an instance of String, the
> metaclass should be a virtual class extending String itself.
> 
> Once again only JRuby produces the expected result.
> 
> $ irb -r metaid
> irb(main):001:0> String.new.metaclass.superclass == String
> => false
> 
> $ jirb -r metaid
> irb(main):001:0> String.new.metaclass.superclass == String
> => true

[Quoted that much to make comparison easier.]

I don't see which version you are testing here.  Here are my results for
Sun-sparc-solaris2.9 for the versions of ruby I have:

brains hgs 31 %> ruby --version
ruby 1.8.6 (2007-09-24 patchlevel 111) [sparc-solaris2.9]
brains hgs 32 %> irb -v
irb 0.9.5(05/04/13)
brains hgs 33 %> irb -r metaid
irb(main):001:0> String.metaclass
=> #<Class:String>
irb(main):002:0> String.metaclass.superclass
=> #<Class:Class>
irb(main):003:0> String.metaclass.superclass == Object.metaclass
=> false
irb(main):004:0> Object.metaclass
=> #<Class:Object>
irb(main):005:0> quit
brains hgs 34 %> cd /scratch/hgs
brains hgs 35 %> ls /scratch/hgs/local/bin/irb
/scratch/hgs/local/bin/irb
brains hgs 36 %> /scratch/hgs/local/bin/ruby --version
ruby 1.9.0 (2007-10-07 patchlevel 0) [sparc-solaris2.9]
brains hgs 37 %> /scratch/hgs/local/bin/irb -v
irb 0.9.5(05/04/13)
brains hgs 38 %> /scratch/hgs/local/bin/irb
irb(main):001:0> require '/home/hgs/metaid.rb'
=> true
irb(main):002:0> String.metaclass
=> #<Class:String>
irb(main):003:0> String.metaclass.superclass
=> #<Class:Object>
irb(main):004:0> String.metaclass.superclass == Object.metaclass
=> true
irb(main):005:0> Object.metaclass
=> #<Class:Object>
irb(main):006:0> quit
brains hgs 39 %>

So I think you are using 1.8.x
        HTH
        Hugh