From: Jean-Hugues ROBERT <jean_hugues_robert@...>
Date: 2004-04-29T23:33:20+09:00
Subject: Re: Pointers in Ruby

At 21:59 29/04/2004 +0900, you wrote:
>Hi --
>
>Jean-Hugues ROBERT <jean_hugues_robert@yahoo.com> writes:
>
> > Hi,
> >
> > I am coining a Pointer class in Ruby. Kind of a C pointer, more
> > like a C++ smart pointer actually. Should work for any lvalue.
> >
> > Any previous art ?
>
>Well, there's the fact that all variables in Ruby are already
>references :-)  So you can do things like:
>
>   e = ENV
>   e["USERNAME"] = "Ruby"
>   p ENV["USERNAME"]      # "Ruby"
>
>Can you give an example of something you would need the extra layer
>of reference for?
>
>
>David
>
>--
>David A. Black
>dblack@wobblini.net

"Any problem in computer science can be solved with another level
of indirection." - David Wheeler.
See http://c2.com/cgi/wiki?ButlerLampson

I need that Pointer class to implement a more complex one called
LogicVariable. A logic variable potentially references a
regular variable and provide addition behavior. Mainly a "match(a,b)"
method. Match does Prolog style pattern matching. A LogicVariable
can be either bound to some value, or free. When it is free it
acts as a wild card and will be assigned whatever value matches
in the other parameter of match.

Example:
def test()

   a = [[1],"z"]
   b = 0
   logic_b = LogicVariable.new( ref{":b"})
   logic_b.free!
   match( a, [[logic_v],Free])
   p b # => 1

I need the pointer to assign b as a side effect of match().

lvalues are one of the few things that are not objects in Ruby
(yet), which is why I needed a special class to manipulate them.

Yours,

Jean-Hugues


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