From: Claudio Jeker <cjeker@...>
Date: 2006-02-09T08:35:08+09:00
Subject: Re: boolean annoyance

On Thu, Feb 09, 2006 at 07:35:08AM +0900, Alexis Reigel wrote:
> When I started using ruby I had exactly the same problem as you, porting
> some c code to ruby that was checking some flags. I didn't get to the
> solution myself, as I never ever thought of 0 being true.
> But once you see the advantages of it you'll really appreciate that
> convention.
> In c you do: (flags & 0x01)
> In ruby you do: (flags & 0x01 == 0) or (flags & 0x01).nonzero?
> Or even nicer: flags[0x01]

Does flags[0x01] work with any kind of mask. I thought that flags[3] would
return the value of bit 3 and not the value of bit 0 and 1...
and from the ruby reference Bignum#[] returns the nth bit a 0 or 1 and so
your flags[0x01] would suffer the same way as (flags & 0x01).

> 
> 
> Shortly there was a discussion about the same topic on this list ("nil
> != []"). I'll cite two convincing postings:
> 
> 
> matthew smillie.said:
> <quote>
> 0 *the integer* is only false by convention, and it's a convention
> confined to programming, originating (unless I'm mistaken) from
> languages which didn't define specific 'true' and 'false' logcial
> values separate from integer math.  0's used in some logical  notations
> as a symbol for 'false', but it's unlikely that anyone  familiar with
> formal logic will tell you those 0's are the same 0's  you get from "2 - 2".
> 
> There's no doubt that the convention's been made very useful, but
> there's really no logical basis for equating any particular symbol to
> true or false truth values over any other.
> </quote>

I don't believe that 0 is originating from programming languages but
actually came from the boolean algebra itself. In a binary domain it is
natural to make 0 false. (a && !a == 0 or if converted into the
set-theory doing a intersection of a set A and the complementary set !A
results in the empty set which is normaly written as some kind of 0).
OK doing set algebra in ascii sucks but I think it is parsable.

> 
> 
> amrangaye said:
> <quote>
> One example of this that tripped me up today is the regular expression
> match operator (=~), which returns (0-based) the index of a match, or
> nil otherwise. If 0 was false, you couldn't do:
> 
> if str =~ /^Hello/
> </quote>
> 

OK this is a valid argument against changing behaviour because it would
cause a major regression to existing scripts. I think I have to swallow
this pill and change my coding stile for ruby. Doing binary protocols in
ruby is a bit more challenging than expected.

-- 
:wq Claudio