Re: Seeing if two numbers have the same sign

[f00li5h]

sub same_sign{
  my($left, $right) =@_;
  (0 <=> $left) == (0<=> $right);

}

[WoodyWeaver]

What is the goal here?

Using <=> is clever, I think. And by that I mean that it invokes a less common set of symbols to come to a result in a surprising and elegant way.

I'm not sure that is good, though. Assuming that if either variable is zero you should return 0, my first thought was

if ($left > 0) {
  if ($right > 0) { # both pos
    return 1
  }
} elsif ($left < 0) {
  if ($right < 0) { # both neg
    return 1
  }
}
return 0;

That is, anchor one, see if the other is the same, and if so return 1; otherwise, fall through and return 0.

I think this is bad because its a whole bunch of lines. On the other hand, I think its good because its dead obvious, and probably pretty fast (fewer compares and jumps than even the double '<=>' version).

ymmv. "What is good?", asked jesting Pilate, not waiting for an answer.

--woody

[f00li5h]

Using the shuttles I'm basiclaly asking "Do these 2 numbers compare to zero the same way"

Personally i'm a fan of the $left * $right > 0 solution, it has a nice mathy feel. although may have issues for massive numbers etc (Corion++ on that count)

[shmem]

Nice, f00li5h++

sub same_sign {
  (0 <=> $_[0]) == (0 <=> $_[1])
                ||
       (! $_[0] || ! $_[1]);
}

to check for either operand being somewhat false ;-)