sub mk_accessors {
    my ( $class, @accessors ) = @_;
    foreach my $accessor (@accessors) {
        no strict 'refs';
        my $key  = "$class\::$accessor";
        *$key = sub {
            my $self = shift;
            return $self->{$key} unless @_;
            $self->{$key} = shift;
            return $self;
        };
    }
}