From: Robert Klemme <shortcutter@...>
Date: 2008-06-19T22:41:34+09:00
Subject: Re: Why metaclasses?

2008/6/19 James Coglan <jcoglan@googlemail.com>:
> So anyway, this question has been really bugging me: in Ruby, how come
> metaclasses are just that: classes? Given that you cannot instantiate them,

13:32:55 OPSC_Gold_bas_dev_R1.2.2$ irb
Ruby version 1.8.6
irb(main):001:0> x = Class.new
=> #<Class:0x7ff9ece4>
irb(main):002:0> o = x.new
=> #<#<Class:0x7ff9ece4>:0x7ff9b56c>
irb(main):003:0> o.class
=> #<Class:0x7ff9ece4>
irb(main):004:0> o.class == x
=> true
irb(main):005:0> x === o
=> true
irb(main):006:0> y = Class.new x
=> #<Class:0x7ff81dc4>
irb(main):007:0> y.superclass
=> #<Class:0x7ff9ece4>
irb(main):008:0> y.superclass == x
=> true
irb(main):009:0> u = y.new
=> #<#<Class:0x7ff81dc4>:0x7ff77518>
irb(main):010:0> x === u
=> true
irb(main):011:0> y === u
=> true

irb(main):012:0> m = Module.new
=> #<Module:0x7ff6e058>
irb(main):013:0> y.class_eval { include m }
=> #<Class:0x7ff81dc4>
irb(main):014:0> m === u
=> true
irb(main):015:0> y.ancestors
=> [#<Class:0x7ff81dc4>, #<Module:0x7ff6e058>, #<Class:0x7ff9ece4>,
Object, Kernel]
irb(main):016:0>

> is there any reason why they need to be classes instead of just modules? I
> want this release to be as close to Ruby as possible so if I've seriously
> misunderstood something I'd rather be put right.

See above. :-)

Kind regards

robert

-- 
use.inject do |as, often| as.you_can - without end