sub swap {
  my ($a, $b) = \(@_);
  
  ( $$a, $$b ) = ( $$b, $$a );  
}
 
my ($x,$y)=(42,666);
 
$\="\n";
print "($x,$y)";    #> (42,666)
swap($x,$y);
print "($x,$y)";    #> (666,42)

##</code><code>##

sub swap {
  my $a = \shift;
  my $b = \shift;
  
  ( $$a, $$b ) = ( $$b, $$a );  
}


##</code><code>##

sub swap { 
   ($_[0], $_[1] ) = ( $_[1], $_[0] ); 
}