我已经把一个简单的C++事件模式,其允许执行以下操作:鲁棒C++事件模式
struct Emitter {
Event<float> ev;
void triggerEvent() { ev.fire(42.0); }
};
struct Listener {
void gotEvent(float x) { ... }
};
int main() {
// event source and listener unaware of each other's existence
Emitter emitter();
Listener listener();
// hook them up
emitterA.ev.addSubscriber(&listener, &Listener::gotEvent);
{
Listener listener2();
emitter.ev.addSubscriber(&listener2, &Listener::gotEvent);
emitter.triggerEvent();
emitter.ev.removeSubscriber(&listener2);
//^PROBLEM!
}
emitter.triggerEvent();
emitter.ev.removeSubscriber(&listener1);
}
的问题是,该显影剂需要手动除去每个用户,否则事件的火()在遍历所有用户的迭代中,最终会触发一个对象的方法,这个对象可能存在也可能不存在。
下面是完整的代码,从一个工作示例在一起:http://coliru.stacked-crooked.com/a/8bb20dacf50bf073
我会在下面贴了后人。
如果我注释掉违规行99,它仍然有效!但这显然只是因为内存尚未被覆盖。
这是一个危险的错误,因为它可能处于休眠状态。
我怎样才能以这种方式进行编码,而不会让我接触到这个潜在的UB错误?
有什么办法我行35 ..
template<class... Args>
class Event {
:
void fire(Args... args) {
for(auto& f : subscribers)
f->call(args...);
如果每个用户仍然存在
能在某种程度上检测......
,同时仍保留的事实,发射器和用户不知道彼此的存在?
完整列表:
#include <vector>
#include <iostream>
#include <algorithm>
#include <memory>
using namespace std;
template<class... Args>
class SubscriberBase {
public:
virtual void call(Args... args) = 0;
virtual bool instanceIs(void* t) = 0;
virtual ~SubscriberBase() { };
};
template<class T, class... Args>
class Subscriber : public SubscriberBase<Args...> {
private:
T* t;
void(T::*f)(Args...);
public:
Subscriber(T* _t, void(T::*_f)(Args...)) : t(_t), f(_f) { }
void call(Args... args) final { (t->*f)(args...); }
bool instanceIs(void* _t) final { return _t == (void*)t; }
~Subscriber() final { cout << "~Subscriber() hit! \n"; }
};
template<class... Args>
class Event {
private:
using SmartBasePointer = unique_ptr<SubscriberBase<Args...>>;
std::vector<SmartBasePointer> subscribers;
public:
void fire(Args... args) {
for(auto& f : subscribers)
f->call(args...);
}
template<class T>
void addSubscriber(T* t, void(T::*f)(Args... args)) {
auto s = new Subscriber <T, Args...>(t, f);
subscribers.push_back(SmartBasePointer(s));
}
template<class T>
void removeSubscriber(T* t) {
auto to_remove = std::remove_if(
subscribers.begin(),
subscribers.end(),
[t](auto& s) { return s->instanceIs((void*)t); }
);
subscribers.erase(to_remove, subscribers.end());
}
};
// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
// example usage:
class Emitter {
private:
string name;
public:
Event<float> eventFloat;
Event<bool, int> eventB;
Emitter(string _name) : name(_name) { }
void triggerEvent() {
cout << name << "::triggerEvent() ~ Firing event with: 42\n";
eventFloat.fire(42.0f);
}
};
struct Listener {
string name;
Listener(string _name)
: name(_name) {
cout << name << "()\n";
}
~Listener() {
cout << "~" << name << "()\n";
//emitter.eventFloat.removeSubscriber(this);
}
void gotEvent(float x) { cout << name <<"::gotEvent hit with value: " << x << endl; }
};
int main() {
// event source and listener unaware of each other's existence
Emitter emitterA("emitterA");
Listener listener1("listener1");
// hook them up
emitterA.eventFloat.addSubscriber(&listener1, &Listener::gotEvent);
{
Listener listener2("listener2");
emitterA.eventFloat.addSubscriber(&listener2, &Listener::gotEvent);
emitterA.triggerEvent();
//emitterA.eventFloat.removeSubscriber(&listener2); // hmm this is awkward
}
emitterA.triggerEvent();
emitterA.eventFloat.removeSubscriber(&listener1);
emitterA.triggerEvent();
return 0;
}