From: Cyent <cyent@...>
Date: 2005-05-08T16:04:29+09:00
Subject: No Thing Here vs Uninitialized and RCR 303

I'm observing a general trend in the responses to RCR 303.

The first and most striking is -w. I always, utterly and without fail, use
-w and had assumed incorrectly that everyone else did. (But then I always
use -W -Wall on gcc as well)

This fact I find curious given the storm of but "RCR 303 might mask a bug"
responses.

Now let us consider when a nil does arise in ruby....

Nil arises in several places that I can think of.

The most obvious case, and the case I think most people are concerned
about, is when referencing an uninitialized variable.

This case is flagged by -w, and hence I had mentally disregarded the
possibility when I wrote RCR 303.

The next case is when nil is returned by something like a regex match or
an index out of bounds.

The third case is when explicit set by the programmer, typically as a
default parameter to a method.

The fourth case is to get around the lexical scoping umfeature of rubies
local variables.

def foo
  my_var = nil
  box.each do |e| 
    my_var = e if e.blah
  end

  use_var( my_var)
end

This is another case of "nil means uninitialized".

So what we have is a "nil" is a little too busy, means too much, is
overloaded too heavily.

It means "uninitialized".

It also means "no thing here" (as in return from regexp match (no
MatchData here), index out of bounds (no Array element here), and nil as a
default value.)

I perfectly agree that "uninitialized" should throw a
NoMethodError. Indeed I doubt if it should respond to some of the
methods it does respond to currently. I even think -w is too friendly, I
would prefer it to throw than to just warn.

What I as thinking of by RCR 303 is nil as "no thing here" should respond
to all methods, do nothing and return "no thing here".

So perhaps I should retract RCR 303 and created a new one suggesting  and
differentiation between "uninitialized" and "no thing here", and
effectively RCR-303 for "no thing here".

I would welcome suggestions as to how to craft this new RCR. 


-- 
John Carter

The Cybernetic Entomologist - cyent@xtra.co.nz

http://geocities.yahoo.com/cy_ent

I'm becoming less and less convinced of humans as rational beings.
I suspect we are merely meme collectors, and the reason meme is only
kept on to help count our change.