From: Artur Merke <merke@...>
Date: 2004-12-10T21:22:31+09:00
Subject: Re: adding object attributes

Thanx David, that's the solution, and even fits into one line
for several attributes ;-)

class << b; attr_accessor :dummy, :dummy2 end

Artur

On Fri, 10 Dec 2004, David A. Black wrote:
> Hi --
>
> On Fri, 10 Dec 2004, Artur Merke wrote:
>
> > Hi
> >
> > class A
> >  attr_accessor :a
> > end
> >
> > a= A.new
> > b= A.new
> >
> > #this adds a new attribute to the object 'b'
> > def b.dummy
> >  @dummy
> > end
> > def b.dummy=(val)
> >  @dummy= val
> > end
> >
> > b.dummy= "hello world"
> > print "\n", b.dummy
> >
> > Is there a shorthand notation for adding attributes to an object?
> >
> > For example one could think of the equivalent of adding an attribute to a
> > class, like
> >
> > b.attr_accessor(:dummy)  #illegal in ruby
> >
> > Of course I could define a sort of public 'attr_accessor' for the class
> > 'A' by myself, but I do NOT want to change/extend the class, only some objects.
> >
> > any suggestions?
>
> What you want to do is use attr_accessor -- but, as you say, not in
> 'A', but rather in the singleton class of 'b'.  You would do this like
> this:
>
>     class << b
>       attr_accessor :dummy
>     end
>
> (A singleton class is anonymous, so you have to use the "<< object"
> notation to "fish" for it from the object whose singleton class it
> is.)
>
> In fact, when you do:
>
>    def b.dummy ...
>
> you are inserting a method into exactly the same class.  Opening up
> the class, however, makes it possible to use class methods, like
> attr_accessor.
>
>
> David
>
> --
> David A. Black
> dblack@wobblini.net
>
>
>