From: thomass@... (Thomas)
Date: 2002-01-20T19:53:57+09:00
Subject: Re: $_ as default parameter for a function

Could you, or someone else explain whats going on below?

Maybe I should emphasize what it is I want to do! I'm working on a
ZipInputStream and a ZipOutputStream, and I would very much like these
classes to work like IO, of course. Ideally I would like to have been
able to provide a few very basic methods for input and output, and IO
would then provide the rest, but IO does not appear to be suited for
that, though please tell me if I'm wrong.

So rather than subclassing IO I have implemented two modules
InputStream and OutputStream that you can mixin. In order to work like
the i/o methods in IO, I often need to fall back to the value of $_ in
the calling scope as a default value.

Any ideas?

Thomas

Mathieu Bouchard <matju@sympatico.ca> wrote in message 

> Yes, $_ is a local, and yes, built-in methods have access to the $_ of the
> caller. Here's an excerpt from MetaRuby 0.7 in module HollowString:
> 
> 	# it's your own fault for using ~
> 	def ~
> 		# setting up quantum superposition
> 		r,w = IO.pipe
> 		if not fork then
> 			set_trace_func(proc{|*a|
> 				w.puts(eval("$_", a[4]).inspect)
> 				exit!
> 			})
> 		else
> 			Process.wait
> 			eval(r.readline) =~ self.to_str 
> 		end
> 	end