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

my %bigHash   = map {$_ => undef} 1 .. 1e3;
my @resetEach = keys %bigHash;
my ($key)     = each %bigHash;
my $count     = keys %bigHash;
my ($key2)    = each %bigHash;

print "First key '$key', second '$key2'\n";

cmpthese (
    -1,
    {
        scalarKeys => sub {scalar keys %bigHash},
        listKeys   => sub {() = keys %bigHash},
    }
);

##</code><code>##

First key '559', second '559'
                 Rate   listKeys scalarKeys
listKeys       5184/s         --      -100%
scalarKeys 15969899/s    307964%         --