title: Get error when I push element onto vector
body: <p>I get a <code>is implicitly deleted because the default definition would be ill-formed</code> error with below code when I want to add the element to the vector with <code>container.push_back(tmp);</code>, why is this?
  My code:</p>
  
  <pre><code>#include &lt;vector&gt;
  #include &lt;mutex&gt;
  class A {
      public:
      A(){}
      ~A(){}
  };
  class my_t {
      private:
          bool busy;
          bool alive;
          std::mutex bmtx;
          std::mutex amtx;
      public:
          my_t(){std::lock_guard&lt;std::mutex&gt;lock(bmtx);busy=false;}
          ~my_t(){}
          A* conn; 
          void take(void) {std::lock_guard&lt;std::mutex&gt;lock(bmtx);busy=true; }
          void give(void) {std::lock_guard&lt;std::mutex&gt;lock(bmtx);busy=false; }
          bool busy_get(void) {return busy;}
          void set_online(void){ std::lock_guard&lt;std::mutex&gt;lock(amtx); alive=true; }
          void set_OFFLINE(void) {std::lock_guard&lt;std::mutex&gt;lock(amtx); alive=false; }
          bool alive_get(void) {return alive;}
  
  };
  
  class app {
      private:
          std::vector&lt;my_t&gt; container;
      public: 
          app();
          ~app();
  };
  app::app() {
      my_t tmp;
      tmp.conn = new A();
      if (tmp.conn)
          tmp.set_online();
      container.push_back(tmp);
  
  
  }
  int main(void) {}
  </code></pre>
  
  <p>or on Coliru: <a href="https://coliru.stacked-crooked.com/a/11625c77383df80c" rel="nofollow noreferrer">https://coliru.stacked-crooked.com/a/11625c77383df80c</a></p>