use strict;
use warnings;
use v5.28;

my $hi = Hello->new();

$hi->memorize('Hi, how are you?');
$hi->say();

package Hello;

sub new {
    bless { memory => [] }, shift
}

sub memorize {
    # push on reference is forbidden
    push @{shift->{memory}}, shift
}

sub say {
    print join('. ', @{shift->{memory}}), "\n"
}