title: What is std::decay and when it should be used?
body: <p>What are the reasons for the existence of <a href="http://en.cppreference.com/w/cpp/types/decay"><code>std::decay</code></a>?
  In what situations is <a href="http://en.cppreference.com/w/cpp/types/decay"><code>std::decay</code></a> useful?</p>