A "reference" means a reference to a space in (perl interpreter) memory. It's like the number of a pigeon-hole/post-office box: the number(=address) remains the same but the contents may change any time. And that change will be reflected on all those places in your script where you read that reference. For example:

my @arr = (1,2,3);
my $ref = \@arr; # or just [1,2,3]
print $ref->[0]; # 1
$arr[0] = 42;
print $ref->[0]; # 42

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No matter which part of your script you pass that reference, when you do $arr[0] = 42; all these places will automatically see the new value 42. Because you gave them a pigeon-hole (PH) number. They look for the contents of that PH. And when you change the contents, they will see that change.

In the loop foreach my $other you keep changing the contents of just one PH you asked for, outside the loop. Its address remains the same, set in my $piece; So, as anonymonk says, create a new reference each time you loop. The PH will be preserved in memory and in your hash even when my $piece goes out of scope. Because you passed that PH number to your hash, it remains alive (here you may want to read Perl and Garbage Collection).

This is a very powerful feature. You create a data structure in memory, like you do. Then get a reference (its PH number) and then pass that to any part of your (single-threaded) program, e.g. subs, which need to read or write onto that data structure. All changes will be communicated immediately to all clients.

Here is some fun:

use strict; use warnings;
use Data::Dumper;
my $joe;
$joe->{name} = 'joe';
$joe->{age} = 42;
my $mary;
$mary->{name} = 'mary';
$mary->{age} = 43;
my $peter;
$peter->{name} = 'peter';
$peter->{age} = 100;

my @children = ($joe, $mary);
my @family = ($mary, $peter, $joe);
my @males = ($joe, $peter);

## oops, Joe is actually written as John
$joe->{name} = 'john';

print Dumper(@children);
print Dumper(@family);
print Dumper(@males);

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bw, bliako

In reply to Re: Unwanted cloning of array elements by bliako
in thread Unwanted cloning of array elements by oakbox

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