From: Robert Klemme <bob.news@...>
Date: 2004-04-30T00:29:03+09:00
Subject: Re: Pointers in Ruby


"Jean-Hugues ROBERT" <jean_hugues_robert@yahoo.com> schrieb im Newsbeitrag
news:6.0.1.1.0.20040429160830.01b31568@pop.mail.yahoo.com...
> At 19:14 29/04/2004 +0900, you wrote:
>
> >"Jean-Hugues ROBERT" <jean_hugues_robert@yahoo.com> schrieb im
Newsbeitrag
> >news:6.0.1.1.0.20040429071924.01cd1ef0@pop.mail.yahoo.com...
> > > 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.
> >
> >Care to share what usage you envision for this?
> >
> >Btw: this rather looks like a reference than a pointer.  As far as I
> >understand, you create an alias for some variable (possibly a local
var)
> >as a handle to modify it from outside the original scope.  Is that
> >correct?
> >
> >     robert
>
> Correct. But it should works for any lvalue not just variables.
> i.e. ref{"a_hash[3]"} for example.
>
>
> I initially named it a reference. But, references are usually
automatically
> dereferenced (they are more transparent than pointers).
>
> I could no find a way to do this in Ruby. That is why I am using the
> []() accessor to get the referenced value.

I'd simply use ordinary methods in the absence of an appropriate operator
that you can use.

class Pointer
  def deref() ...
  def deref=(x) ...
end

That's much more readable although a bit more typing.  IMHO using [] makes
it unnecessary difficult since it raises other associations.

> This is very similar to
> what you do in C with a pointer using * (content of). So, I eventually
> renamed the class Pointer.

I guess you mean "SomeType& operator*() const" etc. in C++.

> Now, I may be wrong about the difference between a pointer and a
reference
> and I would be happy to change the code to something better.

For the scenario you describe in the other posting I'd rather choose
another approach, like holding all values in a hash and using symbols to
reference them.  That way, you can manipulate them easier IMHO.  But that
might be a matter of taste and of course I don't now other preconditions
of your app...

Example:

class Var
  def initialize( env, sym )
    @env, @sym = env, sym
  end

  def val; @env[@sym]; end
  def val=(x); @env[@sym] = x; end
end

env = { :x => true, :y => false }

x = Var.new(env, :x)
p x
p x.val

x.val = !x.val
p x
p x.val

Your class LogicVar might even inherit this class.  Or whatever is most
appropriate in your situation.

Regards

    robert