use v5.14;

package Top {
	use Moose;
	has letter => (
		is        => 'ro',
		isa       => Moose::Util::TypeConstraints::enum(['A', 'B']),
		required  => 1,
	);
	sub BUILD {
		my $self  = shift;
		my $class = "Subordinate" . $self->letter;
		$class->meta->rebless_instance($self);
	}
}

package SubordinateA {
	use Moose;
	extends 'Top';
}

package SubordinateB {
	use Moose;
	extends 'Top';
}

print Top->new(letter => "B")->dump;