title: What does [=] mean in C++?
body: <p>I want to know what <code>[=]</code> does? Here's a short example</p>
  
  <pre><code>template &lt;typename T&gt;
  std::function&lt;T (T)&gt; makeConverter(T factor, T offset) {
      return [=] (T input) -&gt; T { return (offset + input) * factor; };
  }
  
  auto milesToKm = makeConverter(1.60936, 0.0);
  </code></pre>
  
  <p>How would the code work with <code>[]</code> instead of <code>[=]</code>?</p>
  
  <p>I assume that</p>
  
  <pre><code>std::function&lt;T (T)&gt;
  </code></pre>
  
  <p>means an function prototype which gets <code>(T)</code> as argument and return type <code>T</code>?</p>