title: When to use C++ forward_list
body: <p>I am kind of new to C++, and reading the book "The C++ Programming Language (4th edition)". When reading chapter of "STL Containers", the book has a introduction to forward_list:</p>
  
  <blockquote>
    <p>A forward_list (a singly-linked list) is basically a list optimized
    for empty and very short lists. An empty forward_list takes up only
    one word. There are surprisingly many uses for lists where most are
    empty (and the rest are very short).</p>
  </blockquote>
  
  <p>I am wondering how short a list is considering short? And could anyone give a simple example to take the advantage of forward_list?</p>