use Benchmark qw( cmpthese );

my %a = map { $_ => 1 } 1..10;
my %b = map { $_ => 1 } 1..100;
my %c = map { $_ => 1 } 1..10000;

cmpthese(-1, {
   a => sub { keys(%a) == 1; },
   b => sub { keys(%b) == 1; },
   c => sub { keys(%c) == 1; },
});