A string is larger than an integer is larger than undef. Proof: 
#! /usr/bin/perl -w
use strict;
use Devel::Size qw(total_size);

my %hash1 = (
    shave  => '',
    the    => '',
    modern => '',
    way    => '',
);

my %hash2 = (
    shave  => 1,
    the    => 1,
    modern => 1,
    way    => 1,
);

my %hash3 = (
    shave  => undef,
    the    => undef,
    modern => undef,
    way    => undef,
);

print "1: " . total_size(\%hash1) . "\n";
print "2: " . total_size(\%hash2) . "\n";
print "3: " . total_size(\%hash3) . "\n";
__END__
1: 309
2: 261
3: 245

[download]
If you want the fastest way to initialize that hash, I believe it is 
my %hash;
undef(@hash{qw(shave the modern way)});

[download]
but your maintenance programmer may have something nasty to say about that.

In reply to Re: Effecicncy of key-only hash by tilly
in thread Effecicncy of key-only hash by brycen

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