title: What is the logic behind the "using" keyword in C++?
body: <p>What is the logic behind the "using" keyword in C++?</p>
  
  <p>It is used in different situations and I am trying to find
  if all those have something in common and there is a reason
  why the "using" keyword is used as such.</p>
  
  <pre><code>using namespace std; // to import namespace in the current namespace
  using T = int; // type alias
  using SuperClass::X; // using super class methods in derived class
  </code></pre>