title: Passing my compar function to std::multiset with C++11
body: <p>I have a std::multiset, which stores std::pair. I want the first attribute to have no constraint on uniqueness, but I want the second one to be unique. So, I decided to pass my own function to multiset, in order to achieve this (if not please let me know).</p>
  
  <p>Based on <a href="https://stackoverflow.com/questions/16497414/c-use-own-class-in-a-multiset-container">this</a> answer, I wrote a similar function but it fails, and I have no idea why (no idea of λ - and I am Greek :) ).</p>
  
  <pre><code>auto f = [](std::pair&lt;float, int&gt;&amp; a, std::pair&lt;float, int&gt;&amp; b) {
    return (a.first &lt; b.first &amp;&amp; a.second != b.second);
  };
  </code></pre>
  
  <p>Error:</p>
  
  <pre><code>error: expression ‘#‘lambda_expr’ not supported by dump_expr#&lt;expression error&gt;’ is not a constant-expression
  sorry, unimplemented: non-static data member initializers
  error: unable to deduce ‘auto’ from ‘&lt;expression error&gt;’
  </code></pre>