カウンター

カウンターを返す関数make_counter()
sub make_counter {
  my $counter = shift;
  sub { $counter++ };
}
実行例
$c1 = make_counter(10);
$c2 = make_counter(20);
print "c1: ", $c1->(), "\n";
print "c2: ", $c2->(), "\n";
print "c2: ", $c2->(), "\n";
print "c1: ", $c1->(), "\n";
実行結果
c1: 10
c2: 20
c2: 21
c1: 11