in reply to Re: $a++ allowed by $a-- is not ! why?
in thread $a++ allowed by $a-- is not ! why?
(what the correct name for this? commutable?).
commutativity involves only one operation.
and at least two operands which get "permuted". thus, it is pointless to ask for commutativity of an unary operation.
$a + $b = $b + $a
the problem is, ++ is not surjective.
or can you find a value for $z so that ++ $z is "Aa0"? no, you can't:
thus, ++ does not have any reverse mapping at all.
my ($z1, $z2) = qw/ z9 Z9 /;
print ++ $z1, ", ", ++ $z2, $/;
but if we only allow either lower case or upper case (not both mixed), the problem nearly disappears:
a problem is that "0" has no preimage.
++: /\A[A-Z]*[0-9]*\z/ -> /\A[A-Z]*[0-9]*\z/
++: /\A[a-z]*[0-9]*\z/ -> /\A[a-z]*[0-9]*\z/
or can you find a value for $z so that ++ $z is "0"? no, you can't. ;D
HTH hehe, finally i was able to apply some knowledge of last years mathematics. hopefully, i am correct. :-)