use strict;
use warnings;
use Benchmark qw(cmpthese);

my $HASHSIZE = 1e3;
my %hash;

test ();

@hash{1..$HASHSIZE} = () x $HASHSIZE;

test ();

sub test {
    my $_keys = keys %hash;
    my $_scalar_keys = scalar(keys %hash);
    my $_scalar = scalar(%hash);
    my $_if = %hash;
    
    print "_keys: $_keys\n";
    print "_scalar_keys: $_scalar_keys\n";
    print "_scalar: $_scalar\n";
    print "_if: $_if\n";
    
    cmpthese(-1,
              {
               _keys => sub {if (keys %hash) { ; }},
               _scalar_keys => sub {if (scalar(keys %hash)) { ; }},
               _scalar => sub {if (scalar(%hash)) { ; }},
               _if => sub {if (%hash) { ; }},
              }
            );
}