From: Robert Klemme <bob.news@...>
Date: 2004-02-28T07:29:45+09:00
Subject: Re: Extensible meta-data ?


"Its Me" <itsme213@hotmail.com> schrieb im Newsbeitrag
news:l9L%b.8114$lS1.3171@fe2.texas.rr.com...
>
> "Robert Klemme" <bob.news@gmx.net> wrote...
> >
> > > And then use this:
> > > class Mine; end meta ... # metadata on Mine
> >
> > I don't think this will work since class...end doesn't return the class.
>
> Correct. I know I could stick in a "self" before the end to make it work,
> but am very curious why it does not return the class. Similarly, I am very
> curious why def...end does not return a useful object (UnboundMethod?
Proc?
> I'm not a guru, but "nil" is not an intuitive return to me).
>
> > > class Mine
> > >    def foo; end meta ...  # metadata on Mine#foo
> > > end
> > >
> > > Thoughts? Am I trying to do something ridiculous?
> >
> > How about this:
> >
> > class Module
> >   def meta(*args)
> >     case args.size
> >       when 0
> >         meta_data[self]
> >       when 1
> >         if args[0].kind_of? Hash

Even nicer:
if Hash === args[0]

> >           meta_data[self].update args[0]
> >         else
> >           meta_data[args[0]]
> >         end
> >       when 2
> >         meta_data[args[0]].update args[1]
> >       else
> >         raise ArgumentError, "Wrong number of args"
> >     end
> >   end
> >
> >   def meta_data
> >     @meta ||= Hash.new {|h,k| h[k] = {}}
> >   end
> > end
> >
> > class Foo
> >   def foo; puts "bar"; end
> >   meta :foo, "method" => "metadata", "foo" => "bar"
> >   meta "class" => "metadata", "foo" => "bar"
> > end
> >
> > p Foo.meta :foo
> > p Foo.meta
>
> I really want to attach Method meta-data to the Method, not to the class.
If
> I can't figure out how to get a handle on the method object, then perhaps
> I'll do something like this.

I tried a bit with instance_method but didn't get the desired results so I
omitted that part.  Now I know what's wrong here: You can't use
UnboundMethod as hash key because the hash value is not dependent on the
class and method identifier but on the id of the UnboundMethod object only:

irb(main):001:0> class Foo; def bar;end; end
=> nil
irb(main):002:0> Foo.instance_method( :bar )
=> #<UnboundMethod: Foo#bar>
irb(main):003:0> a = Foo.instance_method( :bar )
=> #<UnboundMethod: Foo#bar>
irb(main):004:0> b = Foo.instance_method( :bar )
=> #<UnboundMethod: Foo#bar>
irb(main):005:0> a == b
=> true
irb(main):006:0> b == a
=> true
irb(main):007:0> a.hash == b.hash
=> false
irb(main):008:0> a.id
=> 135052720
irb(main):009:0> a.hash
=> 135052720
irb(main):010:0> b.id
=> 135044800
irb(main):011:0> b.hash
=> 135044800

UnboundMethod#hash is broken in
$ ruby --version
ruby 1.8.1 (2003-12-25) [i386-cygwin]

> Thanks for the code; always amazes me how others' experience shows in much
> more efficient coding styles than my own :)

Thanks!  It's always fun to see what differnt solutions are possible with
Ruby.

Kind regards

    robert