From: Robert Klemme <bob.news@...>
Date: 2005-02-11T00:40:07+09:00
Subject: Re: Class of the Instance [was Re: Building a Better Functor]


"Gavin Kistner" <gavin@refinery.com> schrieb im Newsbeitrag
news:eee6f56d3405a57c4480046c35fca189@refinery.com...
> On Feb 10, 2005, at 7:35 AM, Robert Klemme wrote:
> > "Gavin Kistner" <gavin@refinery.com> schrieb im Newsbeitrag
> > news:991b24e67ac5d4902f4b04192210830a@refinery.com...
> >>> Robert Klemme wrote:
> >>>>     class << self;self;end.class_eval do
> >> Is it to add new methods to the instance only, and not all instances
> >> derived from Foo?
> >
> > Exactly.
>
> Coming from Javascript (where every instance is trivially extensible
> directly) that seems somewhat cumbersome.

JavaScript has no classes as far as I know.  Ruby has classes and from
that alone it's obvious that it's a bit more complicated.  Usually when
you define instance methods you do

obj = ....
class <<obj
  def this_is_only_visible_in_a_single_instance() ... end
end

The construction with class<<self;self;end is only needed in order to be
able to drag local variables into the class_eval block.

> Do many people write things like:
>
> class Object
> def instance_class
> class<<self; self; end
> end
> end
>
> in a common library they re-use frequently? Is there an RCR (or has
> there been discussion)

Discussion - a lot, RCR - maybe.

> about adding a simple method like that to the
> language, so you can simply do:
>
> f = Foo.new
> f.instance_class.class_eval{ ... }

class Object
  def instance_class() class<<self;self;end end
end

> ?
>
> Or (what I'm really looking for) perhaps it might be nice to have a
> define_method method that worked directly for instances. Hrm, but what
> would the syntax be? Perhaps that's not such a good idea.

IMHO it's sufficient to have the simplified access to the singleton class.
OTOH, it's not too difficult to obtain that, so...

Regards

    robert