Singel Threaded Ptr from Andrei Alexandrescu talk at CppCon 2014

singlethreadedptr.h

template<typename T>
class SingleThreadedPtr {
    T *m_p;
    mutable unsigned *m_c;
public:
    SingleThreadedPtr();
    explicit SingleThreadedPtr(T *a_p);
    SingleThreadedPtr(SingleThreadedPtr const &a_rhs);
    SingleThreadedPtr(SingleThreadedPtr &&a_rhs);
    ~SingleThreadedPtr();
};

template<typename T>
SingleThreadedPtr<T>::SingleThreadedPtr() : SingleThreadedPtr(nullptr) {}

template<typename T>
SingleThreadedPtr<T>::SingleThreadedPtr(T *a_p) : m_p(a_p), m_c(nullptr) {}

template<typename T>
SingleThreadedPtr<T>::SingleThreadedPtr(SingleThreadedPtr const &rhs) : m_p(rhs.m_p), m_c(rhs.m_c) {
    if (m_p == nullptr) return;
    if (m_c == nullptr) {
        m_c = rhs.m_c = new unsigned(2);
    } else {
        ++*m_c;
    }
}

#if 1

template<typename T>
SingleThreadedPtr<T>::SingleThreadedPtr(SingleThreadedPtr &&rhs) : m_p(rhs.m_p), m_c(rhs.m_c) {
    rhs.m_p = nullptr;
    // rhs.m_c = nullptr; // UNNEEDED
}

template<typename T>
SingleThreadedPtr<T>::~SingleThreadedPtr() {
    if (m_p == nullptr) return;
    if (m_c == nullptr) {
        soSueMe:
        delete m_p;
    } else if (--*m_c == 0u) {
        delete m_c;
        goto soSueMe;
    }
}

#else
template<typename T>
SingleThreadedPtr<T>::SingleThreadedPtr(SingleThreadedPtr &&rhs) : m_p(rhs.m_p), m_c(rhs.m_c) {
    rhs.m_p = nullptr;
    rhs.m_c = nullptr;
}

template<typename T>
SingleThreadedPtr<T>::~SingleThreadedPtr() {
    if (m_c == nullptr) {
        soSueMe: delete m_p;
    } else if (--*m_c == 0u) {
        delete m_c;
        goto soSueMe;
    }
}
#endif

#if 0
// Skip last decrement
template<typename T>
SingleThreadedPtr<T>::~SingleThreadedPtr() {
    if (m_p == nullptr) return;
    if (m_c == nullptr) {
        soSueMe: delete m_p;
    } else if (*m_c == 1u) {
        delete m_c;
        goto soSueMe;
    } else {
        --*m_c;
    }
}
#endif