package Point;
use Carp 'croak';

sub new {        
    croak('…') unless @_ == 3;
    my ( $class, $x, $y ) = @_;
    return bless { x => $x, y => $y } => $class;
}

sub x {
    croak('…') unless @_ == 1 || @_ == 2;
    my $self = shift
    if ( @_ ) {
        $self->{x} = shift;
    }
    return $self->{x};
}

sub y {
    croak('…') unless @_ == 1 || @_ == 2;
    my $self = shift
    if ( @_ ) {
        $self->{y} = shift;
    }
    return $self->{y};
}

sub inverted {
    croak('…') unless @_ == 1;
    my $self = shift;
    return Point->new( $self->y, $self->x );   
}

1;