title: namespace std:: does not contain optional
body: <p>i am doing the Vulkan Tutorial
      <a href="https://vulkan-tutorial.com/" rel="noreferrer">https://vulkan-tutorial.com/</a></p>
  
  <pre><code>#define GLFW_INCLUE_VULKAN
  #include&lt;GLFW/glfw3.h&gt;
  #include&lt;optional&gt;
  
  struct s {
      std::optional&lt;uint32_t&gt; num;//Intellisense Error
  };
  
  int main() {
      return 5;
  }
  </code></pre>
  
  <p>I started with an empty project and added includes and libraries;
  I can compile and run without including std::optional.</p>
  
  <p>When i use std::optional  I get c2039 "optional is not a member of std"</p>
  
  <p>I am running Windows 10, and VisualStudio 2019 </p>
  
  <p>What is going on here ?</p>
  
  <p>thx.</p>