From: Daniel Brockman <daniel@...>
Date: 2005-07-29T09:58:38+09:00
Subject: Re: Idea for Ruby 2.0

Nikolai,

> Lately I've found myself using pseudo-anonymous variables
> a lot, e.g., something like this:
>
> [[1, 2], [2, 3], [3, 4]].each{ |first, _| fs << first }
>
> The idea is that I'm not interested in the second part of
> the internal arrays, only the first.  The lowline works,
> but obviously for one parameter, as it is a
> valid identifier.

Interestingly, blocks can have duplicate argument names,

   {1=>2}.each {|_,_| puts _} #=> 2

but methods can't:

   def foo _,_ ; end #=> SyntaxError

> I was thinking whether Ruby 2.0 should introduce
> I-don't-care-type variables, like Haskell or Prolog has.

As you said, it would be useful when *passing* arguments,
and it's obviously useful in blocks.  I can see how it could
be worthwhile to allow it in method definitions too ---
for symmetry if nothing else.

> It would make all identifiers beginning with a lowline
> invalid, except in parameter-lists,

As others have pointed out, I'd think just one identifer
would need to be reserved: the single-underscore one.

> which could mean too much incompatability with Ruby 1.x,
> but perhaps it's worth at least some thought?

Even reserving just the single-underscore identifier would
mean some incompatibility, but then you *did* put "Ruby 2.0"
in the subject line. :-)

-- 
Daniel Brockman <daniel@brockman.se>

    So really, we all have to ask ourselves:
    Am I waiting for RMS to do this?   --TTN.