From: "Mauricio Fernández" <batsman.geo@...>
Date: 2004-09-16T02:06:37+09:00
Subject: Re: Singleton method on object via define_method?

On Wed, Sep 15, 2004 at 09:49:50PM +0900, Robert Klemme wrote:
> > > >> o = Object.new
> > > => #<Object:0x10184d40>
> > > >> class << o; class << self; def to_s ; "foo" end end end
> > > => nil
> > > >> class << o; class << self;to_s end end
> > > => "foo"
> > > >> class << o; class << self; class << self; end end end
> > > => nil
> > > >> class << o; class << self; to_s end end
> > > => "#<Class:foo>"
> >
> > It's using Module#to_s because the klass of the singleton class is
> > no longer itself... Module#to_s ends up calling
> >  class << o; self.to_s end
> > which you defined before.
> 
> Well yes, but the fact remains that there is a singleton we don't know of,
> do we?  Probably I don't see clearly your point so I'd appreciate it if
> you'd elaborate it.

It is I who doesn't understand what the above is supposed to prove :)
Before creating the singleton class of the singleton of o's singleton
class, to_s returned "foo", afterwards it returns "#<Class:foo>"...
And anyway, nobody forces us to use to_s

batsman@tux-chan:/tmp$ cat dfg.rb
class Class
	# only works for singletons of singletons, will always return
	# true otherwise
    def has_singleton?
        m = "__magic_#{Time.new.to_i}_#{rand(100000)}"
        class_eval do
            remove_method(m) rescue nil
            define_method(m) { }
            begin
                send m
            rescue NameError
                return true
            ensure
                remove_method m
            end
        end
        false
    end
end

o = Object.new
klass = class << o; class << self; self end end
p klass.has_singleton?
class << klass; end
p klass.has_singleton?

batsman@tux-chan:/tmp$ ruby dfg.rb
false
true

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