title: What are constexpr containers in C++17?
body: <p>I want to make a class that has methods like <code>std::map</code>, but it should be sorted at compile time. Which <code>constexpr</code> containers are suited to store  keys <code>template&lt;class K&gt;</code> and values <code>template&lt;class V&gt;</code>?</p>
  
  <p>std::vector does not meet these requirements.</p>
  
  <p>UPD: We found that <code>std::array</code> has a lot of constexpr methods. And it's enough for my problem to use <code>std::array&lt;std::pair&lt;K, V&gt; &gt;</code>.
  But the question holds.</p>