package CloseOver;

use strict;
use warnings;

my $FIXED_STRING = 'fixed_string';  # could be a constant
my %persistent = (42 => { $FIXED_STRING => 123 });

sub something {

    my ($x,
        ) = @_;

    $persistent{$x}{$FIXED_STRING} = rand;

    }

END {
    for my $k (keys %persistent) {
        print "$k: $persistent{$k}{$FIXED_STRING}\n";
        }
    }

1;

##</code><code>##

Win8 Strawberry 5.8.9.5 (32)  Thu 02/18/2021 21:14:15
C:\@Work\Perl\monks\QM
>perl

use strict;
use warnings;

use CloseOver;

CloseOver::something($_) for 1 .. 3;

^Z
42: 123
1: 0.69775390625
3: 0.8636474609375
2: 0.555877685546875