use Data::Dumper;
use strict;
no warnings;
no autovivification;

my $return_from_sub = '{X}{Y}' ; # a result return from some sub
my $to_process = '$x->' . $return_from_sub; # my local def

my $x = {
	Y => {
		Z => 10,
	}
};

# after some regex work on the $to_process
my $lastPart = 'Y' ; # the last part from $to_process
my $base = '$x->{X}' ; # before the $lastPart
my $lastPartIs = "HASH" ; 
my $newData = [qw/a b c/];

my $ref = eval $base || eval "$base = {}"; # whatever it is, just make it referencable if not defined. 
 
if ( $lastPartIs eq "HASH" ) {
	$ref->{"$lastPart"} = $newData; # Remark 1
}
elsif ( $lastPartIs eq "ARRAY" ) {
	$ref->["$lastPart"] = $newData; # Remark 1
}
print Dumper $x;

##</code><code>##

$ref = eval '$base$return_from_sub';
$ref = [/whatever/];

##</code><code>##

$ref = eval '\$refString';
deference( $ref ) = $whatever ;# [] {} ""