title: What is the technical difference between ? & ! in swift language?
body: <p>Can anyone explain in detail about the technical difference between ! &amp; ? literals that we are using in swift language.  Basically in apple developer document they mentioned it as the nil validation but i didn't understand clearly about the logic behind it.  Can you one explain with some real time logic for the same.</p>
  
  <p>Thanks in advance for the user.</p>