In message "[ruby-talk:00320] Re: Arity features for Proc object?"
    on 99/05/17, Yukihiro Matsumoto <matz / netlab.co.jp> writes:

>Well, well, I opened eval.c to see how hard to implement arity and
>arugument check for block evaluation, and then spent about 1 hour, now
>you see, it's done. :-)

I've done already?? How quick your hack is!!

>I defined two methods, Proc#arity, and Method#arity, which return the
>number of required arguments for the Proc and Method objects.  If they
>accepts variable number of arguments, the arity return negative number.

Great! it seems suitable spec.  Is to use Method#arity as follows??

# obj.method(:method_name).arity
# e.g.
	"a".method(:concat).arity  #=> 1 (correct?)

>  proc = Proc.new{|i,| ..}      # explicitly declare single argument
>  proc.call(a,b)

Well, Is this feature - camma-trailing block parameter - documented 
anywhare??

>and
>
>  proc = Proc.new{|i,j| ..}     # more than two arguments
>  proc.call(a,b,c)
>
>will cause ArgumentError exception, just like methods.
>I think it does not break any existing code.

I see.  It is very what I want. 
tons of thanks!!

-- gotoken