Don't make copies.

use DDS;
my $ref = { 1 .. 4 };
my %foo = %{ $ref };
$foo{1} = 6;
Dump( $ref, \%foo );
__END__
$HASH1 = {
           1 => 2,
           3 => 4
         };
$HASH2 = {
           1 => 6,
           3 => 4
         };
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%foo and $ref point to two different hashes. %foo is a shallow copy of has pointed to by $ref. See references quick reference