$ perl -Mstrict -Mwarnings -E '
    my %x;      say scalar keys %x; say scalar values %x;
    my %y = (); say scalar keys %y; say scalar values %y;
'
0
0
0
0

##</code><code>##

#!/usr/bin/env perl

use strict;
use warnings;

use Benchmark qw{cmpthese};

cmpthese -1 => {
    no_assignment => sub { my %hash },
    assignment    => sub { my %hash = () },
};

##</code><code>##

                    Rate    assignment no_assignment
assignment     6672755/s            --          -60%
no_assignment 16770827/s          151%            --