package Player;
#[...]
sub defaults {
    my $self= shift;
    return
        $self->SUPER::defaults(),
        'symbol'   => '_',
        'score'    => 0,
}
#[...]
package Mover;
#[...]
sub defaults {
    my $self= shift;
    return
        $self->SUPER::defaults,
        'symbol' => '?',     # override this in subclasses
        'x'      => 0,       # x-coordinate
        'y'      => 0,       # y-coordinate
        'vx'     => 0,       # velocity in x-direction
        'vy'     => 0,       # velocity in y-direction
        'shown'  => 1,       # still alive?
}
#[...]
package Object;
#[...]
sub defaults {
    return;
}
sub init {
        my ($self, $args) = @_;
        my ($defaults)= { $self->SUPER::defaults() };
        @{$self}{keys %$defaults}= values %$defaults;
        # If %args are given to new(), use those instead
        @{$self}{keys %$args}= values %$args;
}