title: How is optional assignment constexpr in C++ 20?
body: <p>To the internal content of an optional, doesn't the optional require placement new in order to reconstruct the internal in place storage or union? Is there some new feature like placement new in C++ 20 that allows for constexpr assignment of std::optional?</p>
  <pre><code>template&lt; class U = T &gt;
  optional&amp; operator=( U&amp;&amp; value );
  (since C++17)
  (until C++20)
  template&lt; class U = T &gt;
  constexpr optional&amp; operator=( U&amp;&amp; value );
  (since C++20)
  </code></pre>