From: John Carter <john.carter@...>
Date: 2005-05-09T12:36:39+09:00
Subject: Re: No Thing Here vs Uninitialized and RCR 303

On Mon, 9 May 2005, David A. Black wrote:

> Or do you mean instance variables and global variables, which evaluate
> to nil by default prior to being initialized?

Well, that one is clearly a case of nil === "uninitialized"

> Do you mean there's a convention of initializing variables to nil, prior 
> to (say) their use as iterator variables or counters?  If so, that's 
> very different from an uninitialized variable.

Let me bounce that question back to you...

When _you_ personally do that, what do you mean? Do you mean 
"This is ruby's, umm, curious way of declaring local variables, namely by 
initializing them to something. I am initializing this local variable to 
nil. By this I, David A. Black mean (tick one)

   a) This local variable is uninitialized and I wish ruby to throw an
      error if I invoke a method on it before initializing it to
      something meaningful.

   b) This local variable holds "no thing", and doing nothing and
      returning nothing would be an appropriate action on invoking a
      method on it.

Myself, John Carter, would like on some occasions to tick one and on
other occasions to tick the other. Currently, whatever I mean, the
effect is a).

I can, and am currently writing a Nothing class that allows me to
assign NOTHING, the sole instance of my Nothing class to a local
variable in the case you describe.

But I'm running up against the gotcha that deep in "ruby.h" is a macro
RTEST.

Rubies interpretor, eval.c uses RTEST in many places. In "if",
in "unless", in "while", in....

RTEST is 0 (false) in the C speaking world of eval if an ruby
expression evaluates to false or nil.

For my Nothing class to really work well, I would need RTEST to
evaluate to 0 for nil,false and NOTHING.

All Work arounds and suggestions welcome...






John Carter                             Phone : (64)(3) 358 6639
Tait Electronics                        Fax   : (64)(3) 359 4632
PO Box 1645 Christchurch                Email : john.carter@tait.co.nz
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