It is a matter of taste (and style), but I only use
unless without the
else-clause. If you have the
else, then you could just as well use a normal
if and get better readability - it's more like waht everyone is used to.
But in a standalone if (!(some_complicated_expression)) the use of unless lets you remove one pair of parenthesis and lets the poor smuck reading the code have one less thing to worry about.
I would rewrite your example as
$value=20;
if ($divisor!=0){ #so long as the $divisor isn't equal to 0
$value=$value/$divisor; #go ahead and divide $value by $divisor
} else {
$divisor=1; #otherwise set $divisor to 1
}
Now the statement says the same as the comment (in your code it should have been
#unless the $divisor isn't equal to 0 - 'so long' indicates a repetition IMHO).