From: Mark Hubbart <discordantus@...>
Date: 2005-04-30T04:46:07+09:00
Subject: Re: determining when inside 'class << self'

On 4/29/05, Florian Gro� <florgro@gmail.com> wrote:
> Lionel Thiry wrote:
> 
> >>   class << []
> >>     p inside_metaclass? #=> true
> >>   end
> >
> > Sorry for the newbie question, but what does this mean?
> 
> class << obj enters the idioclass of an object which is a class that
> contains method that will only be defined for that particular object.

Florian: Great explanation.

Lionel: If 'class << []' itself seems a little odd to you, read on...

The class << obj notation can be used in ways that you might not
expect. Since ruby syntax is not as ridged as some other languages,
any expression can take the place of 'obj' in that notation. For
example, if you want to create a temporary/mock object of some sort:

def clear
  class << (a = Object.new)
    def inspect() `clear` end
  end
end

(this example was pulled right out of my irbrc)

As you can see, 'a' was assigned to, and then the resulting object was
opened for modification. So this code:

class << []
  # do stuff
end

... just creates an anonymous array and opens it's metaclass (or
idioclass or singleton class or virtual class, whatever). However, the
array is never assigned to a variable, so it will probably be garbage
collected pretty soon. You will probably never see this exact thing in
someone's code, but it is possible.

cheers,
Mark