title: Why constexpr must be static?
body: <p>An attempt to create a member of a struct with constexpr attribute without being static result in a compiler error(see below). Why is that? for a single constant value will I have this value in memory until program is terminatted instead of just scope of struct? should I back to use a macro?</p>
  
  <pre><code>struct foo
  {
    constexpr int n = 10;
    // ...
  };
  
  error: non-static data member cannot be constexpr; did you intend to make it static?
  </code></pre>