From: Markus <markus@...>
Date: 2004-10-13T01:57:07+09:00
Subject: Re: closure's self

On Tue, 2004-10-12 at 09:00, Mikael Brockman wrote:
> "trans.  (T. Onoma)" <transami@runbox.com> writes:
> 
> > Curious thought --- what if I'd like to know the arity of the proc being 
> > executed?
> > 
> >   proc{|x| arity }.call(1)
> > 
> > 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)
> 
> 
> Closures per se don't have selfs -- they're not objects.  Consider

     Ah, but they are Objects (as you make use of below).  It's just
that the binding used when their body is called that of their creation,
not of themselves.


> Here's an extremely ugly kludge:
> 
> | class Proc
> |   alias :real_call :call
> |   
> |   def call *args
> |     old_proc = $current_proc
> |     $current_proc = self
> |     real_call *args
> |     $current_proc = old_proc
> |   end
> | end
> | 
> | (lambda do |x|
> |     puts $current_proc.arity
> |     (lambda do |x, y|
> |         puts $current_proc.arity
> |       end).call nil, nil
> |     puts $current_proc.arity
> |   end).call nil
> 
> (It prints 1, 2, 1.)

    We could make id somewhat nicer if we use the "set_local" defined a
few weeks back back on the list:

WARNING: CODE TYPED DIRECTLY INTO EMAIL USING VAGUELY RECALLED
            EXPERIMENTAL FEATURE FROM ANOTHER E-MAIL THREAD

class Proc
    alias :real_call :call
    def call *args
         binding.set_local("this_proc",self)
         real_call *args
        end
    end

or even something like

class Self_aware_proc << Proc
    def initialize(&block)
         super
         binding.set_local("this_proc",self)
         self
        end
    end

or (IIRC):

class Self_aware_proc << Proc
    def initialize(&block)
         super
         self["this_proc"] = self
        end
    end

-- Markus