From: "David A. Black" <dblack@...>
Date: 2004-07-08T19:53:58+09:00
Subject: Re: Array::index and rindex operator

Hi --

On Thu, 8 Jul 2004, George Ogata wrote:

> "David A. Black" <dblack@wobblini.net> writes:
> 
> > On Wed, 7 Jul 2004, George Ogata wrote:
>
> So since the interpreter can't figure it out on it's own, you'd need
> to give it a kick by providing some syntactic signal, e.g.:
> 
> def x &  # the '&' means "I can take a block"
>   ## ... maybe yield ...
> end
> 
> ....but then ruby has a
> 
> >> "no declarations" philosophy (i.e., no declaring "I take blocks" in
> >> the method definition).
> 
> So in the end all I'm saying is that in an Ideal Magical World of
> Happiness (TM), I think it should complain, but I understand that it's
> not really practical now.

You could come fairly close with something like:

  class NoBlockError < Exception; end

  module Kernel
    def b!
      raise unless block_given?
    end
  end

  class C
    def initialize(x)
      b!
      @x = yield(x) * 10
    end
  end

except it reports the error as from the line in #b! (isn't there some
way around that? I can't remember).  

> >> As for the "left-to-right" view, there's no precedence for this being
> >> silently ignored in the presence of ambiguity, is there?
> >
> > I don't think any existing methods do this; I'm really just
> > speculating about whether or not it would make sense to write a method
> > that way.  I think it would, at an abstract level, but having the
> > method intervene if one calls it ambiguously also makes sense, perhaps
> > more sense at the practical level.
> 
> Hmm, it'd be interesting to see.

It would be a question of something like:

  def m(*args)
    if args.empty?
      # do block-aware version
    else
      # use args
    end
  end


David

-- 
David A. Black
dblack@wobblini.net