From: Mikael Brockman <mikael@...>
Date: 2004-10-13T01:00:56+09:00
Subject: Re: closure's self

"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

| def frob &closure
|   [lambda &closure, lambda &closure]
| end

It gives two Procs with the same closure, but different selves.

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.)