From: han.holl@... (Han Holl)
Date: 2004-02-27T18:04:47+09:00
Subject: Re: Callback

ts <decoux@moulon.inra.fr> wrote in message news:<200402261738.i1QHcl815264@moulon.inra.fr>...
> >>>>> "H" == Han Holl <han.holl@pobox.com> writes:
> 
> H> The following code works, but I was wondering if the creation of the @obj
> H> instance variable is really necessary?
> 
>  The problem is not with the instance variable, but with the evil eval :-)
> 
>  You don't prefer this ?
> 
> svg% cat b.rb
> #!/usr/bin/ruby
> class A
> end
> 
> class B
>    def initialize(k, cb)
>       class << cb; self end.instance_eval do
>          define_method('cassette') { k }
>       end
>    end
> end
> a = A.new
> g = B.new([1,2,3], a)
> puts a.cassette
> svg% 
> 
> svg% b.rb
> 1
> 2
> 3
> svg% 
> 
Oh, yes. I prefer that _very_ much.
But is instance_eval not also an 'evil eval' ?

And define_method isn't in my Pickaxe, nor in ri-0.8a-1, nor in the
doc directory of ruby-1.8.0 not in the ChangeLog.
It _does_ appear in doc/Changelog-1.8.0 of ruby-1.8.1. Strange.

And I kind of wonder about the 'class << cb; self end.' construction.
Wouldn't 'cb.class.' achieve the same ? Both 'b.class.class' and
'class << b; self end.class' return Class in irb.

Many thanks to you, and to Gregory and Pit, for the helpful reactions.