It sounds like you want to be able to create Class::SubClass both from raw args or as a clone of an existing Class instance.

Two things come to mind. You could either add a method to Class to extract the original args:

my $obj = Class->new(...your args...);
my $subobj = Class::SubClass->new($obj->original_args);
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Or add a method to SubClass which extracts the needed args from an instance of obj, so you could have:

my $obj = Class->new(...your args...);
my $subobj = Class::SubClass->clone_from_parent($obj);

package Class::SubClass;
...
sub clone_from_parent {
  my $class = shift;
  my $obj = shift;
  my %args;
  ...set up %args by calling methods on $obj to get info...
  return __PACKAGE__->new(\%args);
}
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It also might be the case that if we knew more about your situation we could recommend better solutions.