[C++知识库]c++新特性11 (12)weak_ptr其他函数

   ~weak_ptr() noexcept {
        this->_Decwref();
    }

    weak_ptr& operator=(const weak_ptr& _Right) noexcept {
        weak_ptr(_Right).swap(*this);
        return *this;
    }

    template <class _Ty2>
    weak_ptr& operator=(const weak_ptr<_Ty2>& _Right) noexcept {
        weak_ptr(_Right).swap(*this);
        return *this;
    }

    weak_ptr& operator=(weak_ptr&& _Right) noexcept {
        weak_ptr(_STD move(_Right)).swap(*this);
        return *this;
    }

    template <class _Ty2>
    weak_ptr& operator=(weak_ptr<_Ty2>&& _Right) noexcept {
        weak_ptr(_STD move(_Right)).swap(*this);
        return *this;
    }

    template <class _Ty2>
    weak_ptr& operator=(const shared_ptr<_Ty2>& _Right) noexcept {
        weak_ptr(_Right).swap(*this);
        return *this;
    }

    void reset() noexcept { // release resource, convert to null weak_ptr object
        weak_ptr{}.swap(*this);
    }

    void swap(weak_ptr& _Other) noexcept {
        this->_Swap(_Other);
    }

    _NODISCARD bool expired() const noexcept {
        return this->use_count() == 0;
    }

    _NODISCARD shared_ptr<_Ty> lock() const noexcept { // convert to shared_ptr
        shared_ptr<_Ty> _Ret;
        (void) _Ret._Construct_from_weak(*this);
        return _Ret;
    }
};

1.1 _Construct_from_weak

template <class _Ty2>
bool _Construct_from_weak(const weak_ptr<_Ty2>& _Other) noexcept {
    // implement shared_ptr's ctor from weak_ptr, and weak_ptr::lock()
    if (_Other._Rep && _Other._Rep->_Incref_nz()) {
        _Ptr = _Other._Ptr;
        _Rep = _Other._Rep;
        return true;
    }

    return false;
}

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