C++类的特种函数生成机制详解

class Widget {
public:
    Widget() = default;
//    ~Widget() = default;
private:
    std::thread m_; // 只移型别
};
unordered_map<int, Widget> mm;
mm.insert({12, Widget()});

class Widget {
public:
    Widget() = default;
    ~Widget() = default;
private:
    std::thread m_; // 只移型别
};
unordered_map<int, Widget> mm;
mm.insert({12, Widget()}); // error!

error: no matching function for call to ‘std::unordered_map<int, Widget>::insert(<brace-enclosed initializer list>)'
   45 |     unordered_map<int, Widget> mm;

// 代码如下：
make_pair(12, Widget());
// 报错如下：
In template: no matching constructor for initialization of '__pair_type' (aka 'pair<int, Widget>')

class Widget {
public:
    Widget() = default;
    Widget(Widget&&) = default;
    ~Widget() = default;
private:
    std::thread m_; // 只移型别
};
unordered_map<int, Widget> mm;
mm.insert({12, Widget()});

class Widget {
public:
    Widget() = default;
private:
    std::mutex m_;
};
unordered_map<int, Widget> mm;
mm.insert({12, Widget()}); // error!

class mutex : private __mutex_base
{
  public:
    /* ... */
    mutex() noexcept = default;
    ~mutex() = default;
    mutex(const mutex&) = delete;
    mutex& operator=(const mutex&) = delete;
	  /* ... */
}

class thread
{
  public:
  thread() noexcept = default;
  thread(const thread&) = delete;
  thread(thread&& __t) noexcept
  { 
    swap(__t);
  }
  ~thread()
  {
    if (joinable())
      std::terminate();
  }
}