From: Trans <transfire@...>
Date: 2006-11-19T02:05:08+09:00
Subject: Re: How to call a class method via the singleton if it exists


Robert Klemme wrote:
> On 18.11.2006 16:56, Trans wrote:
> > I want to call a class level method from the the instance level, but I
> > need it to go through the singeton if it exists. Here is the most basic
> > example:
> >
> >   class X
> >     def self.f ; "A" ; end
> >     def g ; self.class.f ; end
> >   end
> >
> >   x = X.new
> >   x.g  #=> "A"
> >
> >   def x.f; "B"; end
> >   x.g  #=> "A"
> >
> > How do I get the last to return "B"? I know I could use
> > '(class<<self;self;end)' instead of 'self.class', but that will create
> > a singelton even if doesn't exist, which seems very wasteful. Yet I
> > don't recall any (non-hack) way to detect if a singleton is defined. Is
> > there?
> >
> > It would be nice if there was a reference with which we could call up
> > through the class level like this.
>
> Two ideas attached.
>
> 	robert

thanks robert. you helped clarify that unfortunately I've i mis-stated
the problem, there's a contradiction in my example, what I actually
meant was:

   class X
     def self.f ; "A" ; end
     def g ; self.class.f ; end
   end

   x = X.new
   x.g  #=> "A"

   # this should be:
   class << x
     def self.f; "B"; end
   end

   x.g  #=> "A"  # want "B"

so #respond_to? won't help b/c I didn't intend #f to be instance level
method. sorry. what i'm asking for, should make a whole lot more sense
now (i hope)

thanks,
T.