title: C++ functor advantage - holding the state
body: <p>I did study the whole idea of functors, unfortunately I can't understand the real advantage of functors over typical functions. </p>
  
  <p>According to some academic scripts, functors can hold state unlike functions. 
  Can anyone elaborate on this one with some simple, easy to understand example ? </p>
  
  <p>I really can't understand why typical, regular function are not able to do the same. I'm really sorry for this kind of novice question. </p>