From: Nicholas Van Weerdenburg <vanweerd@...>
Date: 2005-01-26T01:24:21+09:00
Subject: Re: Self and Ruby Comparisons

On Tue, 25 Jan 2005 19:30:54 +0900, Robert Klemme <bob.news@gmx.net> wrote:
> 
> "Mathieu Bouchard" <matju@sympatico.ca> schrieb im Newsbeitrag
> news:Pine.LNX.4.21.0501250404130.16754-100000@mondrian.artengine.ca...
> >
> > On Mon, 24 Jan 2005, Csaba Henk wrote:
> >
> > > On 2005-01-23, Mystifier <mystifier@users.berlios.de> wrote:
> > > Btw, I hope you know that Ruby has almost full support for prototype
> > > based programming.
> >
> > Actually, Perl has it better, because you can change the class of an
> > object, and you can change the list of superclasses of any class.
> >
> > However, this is only a slight advantage, as some other people have
> > demonstrated you can do the same for Ruby using not that many lines of C
> > code.
> 
> And if a copy is sufficient you can do this even in pure Ruby:
> 
> class Object
>   def cast(target_class)
>     copy = target_class.allocate
> 
>     instance_variables.each do |var|
>       copy.instance_variable_set(var, instance_variable_get(var))
>     end
> 
>     copy
>   end
> end
> 
> >> class Foo
> >>   attr_accessor :name, :val
> >> end
> => nil
> >> class Bar
> >>   attr_accessor :name, :val
> >> end
> => nil
> >> f=Foo.new
> => #<Foo:0x100c4220>
> >> f.name="nnn"
> => "nnn"
> >> f.val="vvv"
> => "vvv"
> >> b=f.cast Bar
> => #<Bar:0x101a7238 @val="vvv", @name="nnn">
> >> b.class
> => Bar
> 
> > So the only difference is that in Ruby you can't do full prototype-based
> > programming using just 100%-Ruby.
> 
> Do you have a link or explanation that demonstrates the merits of the
> capability to change an instance's class at runtime?  Currently I don't
> have a clue in which situations I would want this.  Thx!
> 
> Kind regards
> 
>     robert
> 
> 

How about migrating legacy objects to new objects at run-time?

Nick
-- 
Nicholas Van Weerdenburg