use strict;
use warnings;
package MyClass; {
    use Tie::Array;
    our @ISA = ('Tie::Array');
    our @data;

    #mandatory methods
    sub TIEARRAY { my $class = shift; bless \@data, $class; @data = @_; return \@data }
    sub FETCH { my ($self, $index ) = @_; print "FETCH($index)\n"; return $data[$index] }
    sub STORE { my ($self, $index, $value) = @_; print "STORE($index)\n"; $data[$index] = $value }
    sub FETCHSIZE { print "<FETCHSIZE> "; return scalar @data }
};
package main;

$|++;
local $" = ", ";

my @x;

tie @x, "MyClass", 0, 0, 0;
my $x = \$x[2];

$$x++;
print "x = (@x)\n";

=begin comment

When I first saw the above, it looked like no matter how many items were tied, they would all refer to the same @MyClass::data internal array.

The next few lines showed that's true: when I tied @y to the same class, @x lost its data; and when an element of @y was changed, the same happened to @x.

=cut

my @y;
tie @y, "MyClass", 0, 0, 0;
print "y = (@y)\n";
print "x = (@x)\n";

$y[1] = 3.14;
print "y = (@y)\n";
print "x = (@x)\n";

untie @y;       # gives a warning: untie attempted while 2 inner references still exist
undef $x;       # uncomment to reduce next warning to 1 instead of 2; comment to keep next warning at 2
untie @x;       # warning, but with only 1 warning if previous line uncommented
print "y = (@y)\n";
print "x = (@x)\n";
# so what's the  second inner reference?

##</code><code>##

=begin comment

When I first saw the above, it looked like no matter how many items were tied, they would all refer to the same @MyClass::data internal array.

The next few lines showed that's true: when I tied @y to the same class, @x lost its data; and when an element of @y was changed, the same happened to @x.

=cut

my @y;
tie @y, "MyClass", 0, 0, 0;
print "y = (@y)\n";
print "x = (@x)\n";

$y[1] = 3.14;
print "y = (@y)\n";
print "x = (@x)\n";

untie @y;       # gives a warning: untie attempted while 2 inner references still exist
undef $x;       # uncomment to reduce next warning to 1 instead of 2
untie @x;       # warning, but with only 1 warning if previous line uncommented
print "y = (@y)\n";
print "x = (@x)\n";
# so what's the  second inner reference?

=begin comment

I wanted to see if I understood enough: make a replica, but use a new anonymous array, rather than having an @data;
MySecond properly keeps @x and @y from interacting.

=cut

package MySecond; {
    use Tie::Array;
    our @ISA = ('Tie::Array');

    #mandatory methods
    sub TIEARRAY { my $class = shift; my $self = bless [], $class; @$self = @_; return $self }
    sub FETCH { my ($self, $index ) = @_; print "FETCH($index)\n"; return $self->[$index] }
    sub STORE { my ($self, $index, $value) = @_; print "STORE($index)\n"; $self->[$index] = $value }
    sub FETCHSIZE { my ($self) = @_; print "<FETCHSIZE> "; return scalar @$self }
};

tie @x, "MySecond", 0, 0, 0;
tie @y, "MySecond", 0, 0, 0;
$x[1] = 2.718;
$y[0] = 0.000281828;
print "|| x = (@x)\n";
print "|| y = (@y)\n";