From: Christoph <chr_news@...>
Date: 2002-04-19T19:08:45+09:00
Subject: Re: calling a class method in "class << obj" context


"Yukihiro Matsumoto" <matz@ruby-lang.org> wrote in message
news:1019173510.282346.16617.nullmailer@picachu.netlab.jp...
> Hi,
>
> In message "calling a class method in "class << obj" context"
>     on 02/04/19, Joel VanderWerf <vjoel@PATH.Berkeley.EDU> writes:
>
> |Why doesn't the singleton class of a inherit the foo method?
>
> Fixed in 1.7; should I backport this behavior?

Playing around a bit I find the new ``meta behavior'' much richer and actually
useful (see Joel's example) however I also don't miss it in 1.6.

/Christoph

----
class Object
  def __meta
    res = class << self; self end
    res.meta_level = 1
    res
  end
  def meta(level = 1)
    if level == 0
      self
    elsif level == 1
      __meta
    else
      __meta.meta(level-1)
    end
  end

  def assert_equal (l,r)
    raise "#{l} != #{l}" unless l == r
  end

  def test_meta_of_singleton
    puts meta(1).superclasses.reverse.join " <| "
    puts meta(2).superclasses.reverse.join " <| "
    puts "meta.superclass == type is meta(k)-invariant"
    puts "\n"

    (1..10).each do |i|
      assert_equal(meta(i).superclass, type.meta(i-1))
    end
  end

end

class Class
  attr_writer :meta_level
  def meta_level
    @meta_level || 0
  end

  def __meta
    res = class << self; self end
    res.meta_level = meta_level + 1
    res
  end

  def superclasses
    res = [self]
    tmp = self
    res << tmp while tmp = tmp.superclass
    res
  end


  def test_meta
    puts meta(0).superclasses.reverse.join " <| "
    puts meta(1).superclasses.reverse.join " <| "
    puts meta(2).superclasses.reverse.join(" <| ")
    puts "meta(2).superclass == type (== Class) is meta(k)-invariant"
    puts "\n"

    (2..10).each do |i|
      assert_equal(meta(i).superclass, Class.meta(i-2))
    end
  end
end



class A;     end
class B < A; end
class C < B; end
# Note calling C.meta(30) at this would result in an exception latter on


Class.test_meta
Module.test_meta
C.test_meta
C.new.test_meta_of_singleton
-----
Object <| Module <| Class
Object <| Module <| Class <| #<Class:Object> <| #<Class:Module> <| #<Class:Class>
Object <| Module <| Class <| #<Class:#<Class:Class>>
meta(2).superclass == type (== Class) is meta(k)-invariant

Object <| Module
Object <| Module <| Class <| #<Class:Object> <| #<Class:Module>
Object <| Module <| Class <| #<Class:#<Class:Module>>
meta(2).superclass == type (== Class) is meta(k)-invariant

Object <| A <| B <| C
Object <| Module <| Class <| #<Class:Object> <| #<Class:A> <| #<Class:B> <| #<Class:C>
Object <| Module <| Class <| #<Class:#<Class:C>>
meta(2).superclass == type (== Class) is meta(k)-invariant

Object <| A <| B <| C <| #<Class:#<C:0xa039c00>>
Object <| Module <| Class <| #<Class:Object> <| #<Class:A> <| #<Class:B> <| #<Class:C> <|
#<Class:#<Class:#<C:0xa039c00>>>
meta.superclass == type is meta(k)-invariant
----