title: Using constexpr when a value is non-const but initialized with a constant expression?
body: <p>For some reason I have a hard time grasping how to correctly use <code>constexpr</code>.</p>
  
  <p>Is the situation described in the title an appropriate place to use it? i.e:</p>
  
  <pre><code>void foo()
  {
      static constexpr const size_t MAX_BUFFER_SIZE = 20 * 1024 * 1024;
  
      constexpr size_t bufferSize = 1024 * 1024; // Initialized with constant expression
      std::vector&lt;char&gt; buffer(bufferSize, ' ');
  
      //...
  
      if (some_condition())
      {
          bufferSize = get_random_value_at_runtime(); // Assigned a new 'non-constexpr' value
          buffer.resize(bufferSize, ' ');
      }
  
      //...   
  }
  </code></pre>
  
  <p>Kind regards!</p>