title: How to set string as value template parameter?
body: <pre><code>template&lt;typename T,T default_value=T{}&gt;
  class Vec{};
  
  Vec&lt;string,"abc"&gt; vs;
  </code></pre>
  
  <p>I get an error:
  'class std::basic_string' is not a valid type for a template non-type parameter</p>