title: Why is there no support for concatenating std::string and std::string_view?
body: <p>Since C++17, we have <a href="http://en.cppreference.com/w/cpp/string/basic_string_view" rel="noreferrer"><code>std::string_view</code></a>, a light-weight view into a contiguous sequence of characters that avoids unnecessary copying of data. Instead of having a <code>const std::string&amp;</code> parameter, it is now often recommended to use <code>std::string_view</code>.</p>
  <p>However, one quickly finds out that switching from <code>const std::string&amp;</code> to <code>std::string_view</code> breaks code that uses string concatenation as there is no support for concatenating <code>std::string</code> and <code>std::string_view</code>:</p>
  <pre><code>std::string{&quot;abc&quot;} + std::string_view{&quot;def&quot;}; // ill-formed (fails to compile)
  std::string_view{&quot;abc&quot;} + std::string{&quot;def&quot;}; // ill-formed (fails to compile)
  </code></pre>
  <p>Why is there no support for concatenating <code>std::string</code> and <code>std::string_view</code> in the standard?</p>