title: How exactly is std::string_view faster than const std::string&?
body: <p><a href="http://en.cppreference.com/w/cpp/string/basic_string_view" rel="noreferrer"><code>std::string_view</code></a> has made it to C++17 and it is widely recommended to use it instead of <code>const std::string&amp;</code>.</p>
  
  <p>One of the reasons is performance.</p>
  
  <p>Can someone explain how <strong>exactly</strong> <code>std::string_view</code> is/will be faster than <code>const std::string&amp;</code> when used as a parameter type? (let's assume no copies in the callee are made)</p>