我想创建一个碰撞系统,其中一个基类代表场景中的一个对象,实现所有的碰撞逻辑,当检测到碰撞时,调用派生类函数进行程序逻辑。我面临的问题是,基类需要了解所有派生类,以便不同函数中的分派(dispatch)能够正常工作。
例子,基类,OnCollisionDetected
会被派生类覆盖,处理碰撞
#include <iostream>
class BasePhysicsObject {
public:
void Collides(BasePhysicsObject * another_object) {
/* ... */
bool collides = true;
if (collides) this->OnCollisionDetected(another_object);
return;
}
/* Function to be overriden */
virtual void OnCollisionDetected(BasePhysicsObject * another_object) = 0;
};
场景中的两个虚拟类,覆盖了函数 OnCollisionDetected(BasePhysicsObject * another_object)
,根据 this
参数将调用分派(dispatch)到适当的函数。
class Fire;
class Player : public BasePhysicsObject {
public:
virtual void OnCollisionDetected(BasePhysicsObject * another_object) {
/* double dispatch to specific implementation */
another_object->OnCollisionDetected(this);
}
virtual void OnCollisionDetected(Fire * fire) {
/* Collision with fire object*/
}
};
class Fire : public BasePhysicsObject {
public:
virtual void OnCollisionDetected(BasePhysicsObject * another_object) {
/* double dispatch to specific implementation */
another_object->OnCollisionDetected(this);
}
virtual void OnCollisionDetected(Player * player) {
/* Collision with player object */
}
};
Main 函数创建两个对象,并检查它们的碰撞。
int main(int argc, char ** argv){
Player * player = new Player();
Fire * fire = new Fire();
fire->Collides(player);
}
最终发生的事情是,从 Collides()
调用的 Fire::OnCollisionDetected(BasePhysicsObject * another_object)
不会调用具有派生类的函数参数即 Player::OnCollisionDetected(Fire * fire)
,而是 Player::OnCollisionDetected(BasePhysicsObject * another_object)
再次回调该函数,导致堆栈溢出.
据我所知,为了使双重分派(dispatch)工作,我需要在所有派生类的基类中声明 OnCollisionDetected(Derived *)
,但这是一个令人生畏的解决方案。还有其他方法吗?
最佳答案
对于双重调度模式,你必须有一个虚拟调度程序。 第一次调度是通过 lhs 实例上的虚拟调用完成的,而不是 rhs 实例的调度:
class BasePhysicsObject {
public:
virtual ~BasePhysicsObject() = default;
virtual void CollideDispatcher(BasePhysicsObject* ) = 0;
// The true collision code.
virtual void OnCollisionDetected(Fire*) = 0;
virtual void OnCollisionDetected(Player*) = 0;
};
class Player : public BasePhysicsObject {
public:
// Always same implementation
// but `this` type is different for each class
// Which allow correct overload resolution
void CollideDispatcher(BasePhysicsObject* rhs) override { rhs->OnCollisionDetected(this); }
void OnCollisionDetected(Fire* rhs) override { /* Player/Fire collision */ }
void OnCollisionDetected(Player* rhs) override { /*Player/Player collision*/ }
};
class Fire : public BasePhysicsObject {
public:
// Always same implementation
// but `this` type is different for each class
// Which allow correct overload resolution
void CollideDispatcher(BasePhysicsObject* rhs) override { rhs->OnCollisionDetected(this); }
void OnCollisionDetected(Fire* rhs) override { /* Fire/Fire collision */ }
virtual void OnCollisionDetected(Player* rhs) override {
// Fire/Player collision:
// might be symmetrical to Player/Fire collision and so:
rhs->OnCollisionDetected(this);
}
};
关于c++ - 使用派生参数覆盖函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/51425626/