title: What is ref struct in definition site
body: <p>I think I've heard a term "ref like struct" in GitHub some time ago. </p>
  
  <p>Now that I have my hands on latest C# version (7.3), I could finally test it my self. So this seems to be a valid code:</p>
  
  <pre><code>public ref struct MyStruct
  {
      int x;
  }
  </code></pre>
  
  <p>I know what are ref locals and ref returns as there is documentation about that. But I could not find documentation about ref struct.</p>
  
  <hr>
  
  <p>Ref structs can not be used on auto properties or fields. They can not be cast to object either. These were empirical findings.</p>
  
  <p>With "Span" background that new c# gave me recently I guessed that ref struct is a stack only struct. That is an struct that never goes on heap. But im not 100% sure.</p>
  
  <p>Im pretty sure there should be a documentation about this but I failed to find it. </p>