Question

我有一个ShapeType，Point，有一些坐标，（1,2），我想在重载的operator（）中使用apply_visitor将坐标（3,4）添加到我的Point，这样点最终成为（4,6）。我的实施在哪里失败了？我认为我的ShapeVisitor类是正确的，但是我收到错误，“apply_visitor”不是CLARK :: Point的成员。

代码如下。

#include "Point_H.hpp"
#include "Shape_H.hpp"
#include "boost/variant.hpp"

typedef boost::variant<Point,Line,Circle> ShapeType;

ShapeType ShapeVariant(){...}

class ShapeVisitor : public boost::static_visitor<> 
{
private:
    double m_dx; // point x coord
    double m_dy; // point y coord

public:    
    ShapeVisitor(double m_dx, double m_dy);
    ~ShapeVisitor();

    // visit a point
    void operator () (Point& p) const
    {
        p.X(p.X() + m_dx);
        p.Y(p.Y() + m_dy);
    }
};

int main()
{   
    using boost::variant;

    ShapeType myShape = ShapeVariant(); // select a Point shape

    Point myPoint(1,2);

    boost::get<Point>(myShape) = myPoint; // assign the point to myShape

    boost::apply_visitor(ShapeVisitor(3,4), myPoint); // trying to add (3,4) to myShape

    cout << myPoint << endl;

    return 0;
}

谢谢！

Answer 1

您缺少包含（编辑：似乎不再需要）
```
#include "boost/variant/static_visitor.hpp"
```
也代替
```
boost::get<Point>(myShape) = myPoint;
```
你只想做
```
myShape = myPoint;
```
否则，如果该变体实际上还不包含Point，您将收到boost::bad_get例外

最后

boost::apply_visitor(ShapeVisitor(3,4), myPoint);

应该是

boost::apply_visitor(ShapeVisitor(3,4), myShape);

显示所有这些点的简单自包含示例如下所示：（现场观看 http://liveworkspace.org/code/33322decb5e6aa2448ad0359c3905e9d ）

#include "boost/variant.hpp"
#include "boost/variant/static_visitor.hpp"

struct Point { int X,Y; };

typedef boost::variant<int,Point> ShapeType;

class ShapeVisitor : public boost::static_visitor<> 
{
private:
    double m_dx; // point x coord
    double m_dy; // point y coord

public:    
    ShapeVisitor(double m_dx, double m_dy) : m_dx(m_dx), m_dy(m_dy) { }

    void operator () (int& p) const { }

    // visit a point
    void operator () (Point& p) const
    {
        p.X += m_dx;
        p.Y += m_dy;
    }
};

int main()
{   
    Point myPoint{ 1,2 };

    ShapeType myShape(myPoint);
    boost::apply_visitor(ShapeVisitor(3,4), myShape);

    myPoint = boost::get<Point>(myShape);
    std::cout << myPoint.X << ", " << myPoint.Y << std::endl;
}

输出：

4, 6

boost :: apply_visitor不是[some]类的成员

1 个答案: