From: Ara.T.Howard@...
Date: 2004-10-13T01:04:41+09:00
Subject: Re: closure's self

On Wed, 13 Oct 2004, trans.  (T. Onoma) wrote:

> Curious thought --- what if I'd like to know the arity of the proc being
> executed?
>
>  proc{|x| arity }.call(1)

like this?

   harp:~ > irb
   irb(main):001:0> cb = proc{|a,b,c| cb.arity}
   => #<Proc:0xb75a0ecc@(irb):1>

   irb(main):002:0> p cb.call(0,1,2)
   3
   => nil

> I see no way to do this, not even with the extended Binding class. I begin to
> wonder (for this and other reasons) if a closure's "self" is doable? (at
> least I think _closure_ is the right "scope" for this)
>
>  proc{|x| this.arity }.call(1)

i don't quite understand this - but i think 'self' must be Object, although you
could probably subclass Proc in a way that it used the 'with' trick or
something, in any case it seems you don't really need 'self' if you can name it
some other way.

maybe you could make a subclass that regeistered itself as a class var when
being called?

something like

   harp:~ > cat b.rb
   class CallBack < Proc
     class << self
       attr :this, true
     end
     def call(*a, &b)
       begin
         self.class.this = self
         super
       ensure
         self.class.this = nil
       end
     end
   end

   CallBack::new{|a| p CallBack::this.arity }.call(42)   #=> 1

if you get my meaning?

cheers.

-a
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