my $var1;
my $var2 = 'val2';

##</code><code>##

#!/usr/bin/env perl -l

use strict;
use warnings;

my $hashref = { a => 1, b => 2 };
my @array = qw{c d e};

use constant {
    HR_ARRAY => [ sort values %$hashref ],
    AREF => \@array,
};

BEGIN { print join ' ', 'B1:', sort(keys %$hashref), @array }
BEGIN { print join ' ', 'B2:', @{+HR_ARRAY}, @{+AREF} }

INIT { @array = qw{f g h} }
INIT { print join ' ', 'I1:', sort(keys %$hashref), @array }
INIT { @array = qw{i j k} }
INIT { print join ' ', 'I2:', @{+HR_ARRAY}, @{+AREF} }

print join ' ', 'R1:', sort(keys %$hashref), @array;
print join ' ', 'R2:', @{+HR_ARRAY}, @{+AREF};

##</code><code>##

B1:
B2:
I1: f g h
I2: i j k
R1: a b c d e
R2: c d e

##</code><code>##

$ perl -E 'use constant AREF => [1..4]; say "@{+AREF}";'
1 2 3 4

$ perl -E 'use constant AREF => [1..4]; say "@{+AREF}"; AREF = []'
Can't modify constant item in scalar assignment at -e line 1, at EOF
Execution of -e aborted due to compilation errors.

$ perl -E 'use constant AREF => [1..4]; say "@{+AREF}"; AREF->[2] = 99; say "@{+AREF}"'
1 2 3 4
1 2 99 4

##</code><code>##

use constant { ONE => 1, ..., FOUR => 4 };
use constant NUM_AREF => [ ONE .. FOUR ];