title: Operator overload syntax clarification
body: <p>Can someone please explain how the following syntax differences change the way the operator works?</p>
  
  <pre><code>T &amp; operator()(type one, type two)
  const T * operator()(type one, type two)
  T &amp; operator()(type one) const
  const T &amp; operator()(type one) const
  </code></pre>