title: Cannot initialize non-const reference from convertible type
body: <p>I cannot initialize a <strong>non-const</strong> reference to type T1 from a convertible type T2. However, I can with a <strong>const</strong> reference.</p>
  
  <pre><code>long l;
  const long long &amp;const_ref = l; // fine
  long long &amp;ref = l;             // error: invalid initialization of reference of
                                  // type 'long long int&amp;' from expression of type
                                  // 'long int'
  </code></pre>
  
  <p>Most problems I encountered were related to r-values that cannot be assigned to a non-const reference. This is not the case here -- can someone explain? Thanks.</p>