Qt Protobuf 可变的获取器

message Point {
    double x = 1;
    double y = 2;
}

message Line {
    Point start = 1;
    Point end = 2;
}

class Line : public QProtobufMessage
{
    const Point &start() const &;
    Point &mutStart() &;
    ...

    const Point &end() const &;
    Point &mutEnd() &;
    ...
}

Line line;

// 将线的起点设置为 (5.0, 5.0)
line.mutStart().setX(5.0);
line.mutStart().setY(5.0);

// 将线的起点设置为 (10.0, 20.0)
line.mutEnd().setX(10.0);
line.mutEnd().setY(20.0);

// 显示 Line 数据
qDebug().nospace() << "start: (" << line.start().x() << "," << line.start().y() << ") "
   "end: (" <<line.end().x()<< "," <<line.end().y()<< ")";