From: Colin Bartlett <colinb2r@...>
Date: 2010-01-22T11:20:24+09:00
Subject: Re: Using underscores for "private" instance variables?

On Wed, Jan 13, 2010 at 4:24 AM, Gregory Brown
<gregory.t.brown@gmail.com> wrote:
> But I agree, @_whatever is ugly and I'm not sure I will introduce it
> into Prawn.   I just understand why the Rails guys did it after having
> a bit of direct experience.
...
> I'm about to do some major refactoring in Prawn in the near future.
> I might play with these thoughts and see where they lead.   If I shake
> anything loose that's worth sharing, I'll write it up on the RBP blog.

Sorry for being a bit late to this thread.
Date (from the 2008-01-17 version?) seems to use @__ca__
as a "hidden" cache for some values:
   def initialize(ajd=0, of=0, sg=ITALY)
     @ajd, @of, @sg = ajd, of, sg
     @__ca__ = {}
   end
Are there any reasons you can't use a hash like that,
or maybe use something like the code below?
Admittedly, the underlying problem isn't eliminated,
just reduced: one has to "agree" not to use @_
(or something similar if @_ is in use or "reserved" for
future use) for a "normal" attribute.
And things like @_.pa2 aren't pretty.
But one thing I like about Ruby is that some things
aren't forbidden, just discouraged by looking ugly
and/or being difficult, so you must think carefully
before using them.

class ExampleClass
  class PrivateAtts
    attr_accessor :private_attribute_1, :pa2
  end
  def initialize() ; @_ = PrivateAtts.new ; end
  def a_method( n ) ; @_.pa2 = n ; end
  def another_method() ; @_.pa2 ; end
end

ex = ExampleClass.new
#=> #<ExampleClass:0x2650600 @_=#<ExampleClass::PrivateAtts:0x26505e0>>
ex.a_method(42)
#=> #<ExampleClass:0x2650600 @_=#<ExampleClass::PrivateAtts:0x26505e0 @pa2=42>>
ex.another_method()
#=> 42