title: 'size_t' vs 'container::size_type'
body: <p>Is there is a difference between <code>size_t</code> and <code>container::size_type</code>?</p>
  
  <p>What I understand is <code>size_t</code> is more generic and can be used for any <code>size_type</code>s.</p>
  
  <p>But is <code>container::size_type</code> optimized for specific kinds of containers?</p>