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#ifndef OBSERVERS_HH
#define OBSERVERS_HH
#include <memory>
#include <vector>
template<typename T>
class Observers {
public:
Observers()
: current_(0), protected_(0), removed_(0) {
}
void add(T* observer) {
if (!observer) return;
for (auto it = observers_.begin(); it != observers_.end(); ++it) {
if (*it == observer) return;
}
observers_.push_back(observer);
}
void remove(T* observer) {
if (!observer) return;
size_t index = 0;
for (; index < observers_.size(); ++index) {
if (observers_[index] == observer) {
if (index < protected_) {
observers_[index] = nullptr;
++removed_;
} else {
observers_.erase(observers_.begin() + index);
}
break;
}
}
}
T* first() {
if (protected_) return nullptr;
if (observers_.empty()) return nullptr;
protected_ = observers_.size();
return observers_[current_];
}
T* next() {
if (current_ >= protected_) return nullptr;
++current_;
if (current_ >= protected_) {
if (removed_) {
for (size_t i = protected_; i > 0; --i) {
if (!observers_[i - 1]) {
observers_.erase(observers_.begin() + i - 1);
if (--removed_ == 0) break;
}
}
}
protected_ = current_ = 0;
return nullptr;
}
auto ret = observers_[current_];
return ret ? ret : next();
}
private:
size_t current_;
size_t protected_;
size_t removed_;
std::vector<T*> observers_;
};
#endif // OBSERVERS_HH
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