Hi, I would use Moo for all your object creation needs if I were you.

package MyBase {
    use Moo;

    has cfg => (
        is      => 'rw',
        default => sub {
            return { on_error => 'exit', output_type => 'text' };
        },
    );
};

package MyChild {
    use Moo;
    extends 'MyBase';

    sub BUILD {
        shift->cfg->{on_error} = 'warn';
    }
};

use strict;
use warnings;
use MyChild;

use Test::More;

ok( my $obj = MyChild->new );
is_deeply( $obj->cfg, { on_error => 'warn', output_type => 'text' } );

done_testing;
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Hope this helps!