多态二进制函数

Polymorphic binary function

本文关键字：函数 二进制 多态      更新时间：2023-10-16

我有三个形状类Circle、Square、ConvexPolygon，并且我有函数

bool ShapesIntersect(const Circle& s1, const Circle& s2);
bool ShapesIntersect(const Circle& s1, const Square& s2);
// ... and the other 7 combinations

我想要一个类似的多态函数

Matrix<bool> ComputeShapeIntersectionMatrix(
const vector<Shape>& shapes1,
const vector<Shape>& shapes2);

调用上面特定于形状的方法来填充相交矩阵。

我认为在c++中不可能做到这一点，但我可以接受任何其他解决方案，只要我可以在不更改计算交集矩阵的代码的情况下添加新的形状类型。

我做了一个多调度器。

如果使用std::variant，它会变得更简单：

using Shape = std::variant<Circle, Square, ConvexPolygon>;
struct intersect
{
template <typename Shape1, typename Shape2>
bool operator()(const Shape1& lhs, const Shape2& rhs) const {
return ShapesIntersect(lhs, rhs);
}
};

Matrix<bool> ComputeShapeIntersectionMatrix(
const vector<Shape>& shapes1,
const vector<Shape>& shapes2)
{
Matrix<bool> res(shapes1.size(), shapes2.size());
for (std::size_t i = 0; i != shapes1.size(); ++i) {
for (std::size_t j = 0; j != shapes2.size(); ++j) {
res[i][j] = std::visit(intersect{}, shapes1[i], shapes2[j]);
}
}
return res;
}

我会这样解决它：

struct Circle;
struct Polygon;
struct Square;
struct Intersector {
virtual bool intersects(const Circle& ) const = 0;
virtual bool intersects(const Polygon& ) const = 0;
virtual bool intersects(const Square& ) const = 0;
};
template<class SHAPE>
struct ShapeIntersetor;
template<>
struct ShapeIntersetor<Square> : Intersector {
const Square& square;
ShapeIntersetor(const Square& square) : square(square) { }
bool intersects(const Circle& ) const override { /* Intersection code */ }
bool intersects(const Polygon& ) const override { /* Intersection code */ }
bool intersects(const Square& ) const override { /* Intersection code */ }
};
// Repeat above for each shape type
struct Shape {
virtual ~Shape() = default;
virtual std::unique_ptr<Intersector> get_intersector() const = 0;
virtual bool intersects(const Intersector& isector) const = 0;
};
struct Polygon : Shape {
std::unique_ptr<Intersector> get_intersector() const override {
return make_unique<ShapeIntersector<Polygon>>(*this);
}
bool intersects(const Intersector& isector) const override {
return isector.intersects(*this);
}
}; 
// Repeat above for each shape type
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