title: Initialize a constexpr array as sum of other two constexpr arrays
body: <p>Given two <code>constexpr</code> arrays (<code>type[N]</code> or <code>std::array&lt;type, N&gt;</code>)</p>
  
  <pre><code>constexpr int A[5] { 0, 1, 2, 3, 4 };
  constexpr int B[5] { 5, 4, 3, 2, 1 };
  </code></pre>
  
  <p>is it possible to initialize a new <code>constexpr</code> array performing an element-wise operation (or <code>constexpr</code> function)?</p>
  
  <p>For example, can this code</p>
  
  <pre><code>constexpr int sum(int i) { return A[i] + B[i]; }
  constexpr int S[5] { sum(0), sum(1), sum(2), sum(3), sum(4) };
  </code></pre>
  
  <p>be rewritten more conveniently in a form that calls <code>sum(i)</code> for every element in <code>S</code>?</p>