title: Is there any application for a constexpr operator++(int) (post-increment)
body: <p>The following code shows how a <code>constexpr operator++()</code> (pre-increment) can be used (<a href="https://wandbox.org/permlink/Ol9kRlqHwob41cY1" rel="nofollow noreferrer" title="live demo">live demo</a>). Now I wonder if there is any usefulness in declaring a post-increment operator as <code>constexpr</code>. I assume that such an operator has no side-effects and is used in a way similar as in the example. (If this is too abstract: I intend to extend my <a href="https://github.com/ClaasBontus/bitset2" rel="nofollow noreferrer">bitset2</a> class and want to know if there would be any benefit if the post-increment operator was <code>constexpr</code>.)</p>
  
  <pre><code>struct S {
    constexpr S( int i ) : m_i( i ) {}
    constexpr S &amp; operator++() {
        ++m_i;
        return *this;
    }
    int m_i;
  };
  
  int main() {
    constexpr auto s1= ++S{3};  
    std::cout &lt;&lt; s1.m_i &lt;&lt; '\n'; // output: 4
  }
  </code></pre>