title: Argument siliently dropped by std::bind?
body: <p>Below code confused me, I expected it can cause compiling error, but actually not. The string<code>my string</code> is silently dropped?</p>
  <p>As I understand TaskFunction expetec two arguments, but when I use std::bind there is one placeholder. Why didn't compiler prevent me assign the bind result to TaskFunction varaible <code>tf</code>?</p>
  <pre><code>#include &lt;string&gt;
  #include &lt;functional&gt;
  #include &lt;iostream&gt;
  
  typedef  std::function&lt; void(int , const std::string&amp;) &gt; TaskFunction;
  
  
  class MyClass {
  
  public:
     void myTask(int i) {
          std::cout &lt;&lt; __FUNCTION__ &lt;&lt; &quot; i = &quot; &lt;&lt; i &lt;&lt; std::endl;
      }
  };
  
  int main()
  {
      MyClass mc;
      TaskFunction tf = std::bind(&amp;MyClass::myTask, &amp;mc, std::placeholders::_1);
      tf(0, &quot;my string&quot;);
      return 0;
  }
  </code></pre>
  <p>Result:</p>
  <pre><code>myTask i = 0
  </code></pre>